department of magnetism · tremal soft magnetic materials is possible to use the diﬀerential...

Chapter 1

DEPARTMENT OF MAGNETISM

1.1 STAFF

1.1.1 Scientific staff

Ivan Baťko, Eva Bystrenová, Pavel Diko, Mar-tina Koneracká, Jozef Kováč, Tibor Krenický,Jozef Marcin, Slavomı́r Maťaš, Marián Mihalik,Zuzana Mitróová, Ivan Škorvánek, Milan Timko(head of department), Natália Tomašovičová,Vlasta Závǐsová, Anton Zentko, Mária Zentková,Kataŕına Zmorayová, Martina Šefč́ıková

1.1.2 PhD students

Mariana Baťová, Frantǐsk Herchl, Mária Lukáčová,Oliver Štrbák

1.1.3 Technical staff

Peter Kuĺık, Kataŕına Paulovičová

1.2 SCIENTIFICACTIVITIES

1.2.1 Introduction

The department is engaged in comprehensive stu-dies on the physical properties of nanocrystallineand amorphous ferromagnetic materials, ferrofluidsand their composites with superconductive partic-les and liquid crystals, fine magnetic properties,organometalic complexes, high–TC superconductorsand intermetallic compounds containing f–elementwith interesting properties at low temperatures likeheavy–fermion behavior and heavy–fermion super-conductivity. Low temperature magnetic and elec-tric research is being extensively developed. Ourresearch is concerned particularly with the condi-tions of existence of the magnetically ordered statein structurally disordered systems and organometal-lic compounds, microstructure parameters limitingmacroscopic properties of bulk high temperature

superconductors, correlation between microstruc-ture and soft magnetic and mechanical behavior ofnanocrystalline aloys, biological application of mag-netic fluids, etc. The magnetic behaviors are investi-gated by using VSM-magnetometers: low field con-figuration with magnetic field up to 80 kA/m for esti-mation of coercive field up to 1 A/m and Curie tem-perature with reproducibility ±0.1K (suitable domi-nantly for magnetic soft materials); high field config-uration working in magnetic field up to 5 MA/m inthe temperature range from 4.2 up to 800 K. For ex-tremal soft magnetic materials is possible to use thedifferential flux gate magnetometer working in mag-netic field up to 20 kA/m in the temperature rangefrom room temperature up to 800 K. The equipmentfor thermal treatment of samples in longitudinal ortransversal external magnetic field up to 0.6 MA/min protective gas or high vacuum up to temperature1000 K is possible too. The apparatus for measure-ment of electrical resistivity of metals and semicon-ductors in temperature range from 4 up to 300 K isavailable. For the preparation and microstructuralcharacterization of samples we can use milling andmixing arrangements (Milles Fritsch: Pulverisette 6,Pulverisette 2), tubular and chamber furnaces withprotecting atmospheres, optical microscopy with im-age processing analysis, thermal analysis complex(DSC calorimeter Perkin Elmer, Setaran TG, DTA,TMA analyser). Close collaboration with physicalinstitutes and universities in Slovakia and abroadduring the existence of department has been estab-lished (Faculty of Science Košice, Institute of PhysicsSAS Bratislava, Charles University Prague, PhysicalInstitute Prague, Physical Institute Warszawa, Insti-tute of Molecular Physics Poznan, Central ResearchInstitute of Physics Budapest, University of Amster-dam, GKSS - Forschungszentrum Geesthacht, J.K.University Linz, TU Vienna, University of Vienna,IPHT Jena, The Leibniz Institute for Solid State andMaterials Research IFW Dresden, The Institute of”Ciencia de Materiales de Barcelona” ICMAB, Ox-ford University, University of Sheffield, WestminsterUniversity, Argonne National Laboratories, Interna-

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8 BIENNIAL REPORT 2003–2004

tional Superconductivity Technology Center Tokyo,The Michigan University, University Liege, TrinityCollege Dublin, etc.).

1.2.2 Projects

Project of Slovak Scientific Grant AgencyVEGA:

2/1168/01 Cooperative phenomena in compoundscontaining f–elementPrincipal investigator: Anton Zentko

2/4050/04 Study of cooperative phenomena andstrong electron correlation in compounds con-taining f–elementsPrincipal investigator: Marián Mihalik

2/4065/03 Structure and magnetic properties oftransition metal based nanocrystalline materi-als prepared by crystallization of amorphousprecursorsPrincipal Investigator: I. Škorvánek

2/1149/01 Magnetic and mechanical properties ofFe- and Co–based nanocrystalline alloysPrincipal investigator: Ivan Škorvánek

2/1145/01 Microstructure parameters limitingmacroscopic properties of bulk high tempera-ture superconductorsPrincipal investigator: Pavel Diko

2/4062/24 REBCO superconducting permanentmagnets with nanoparticle pinning centres.Principal investigator: Pavel Diko

2/3199/03 Magnetic nanoparticles and their rolein different physical systemsPrincipal investigator: Peter Kopčanský

2/7020/00 The study of some physical propertiesof complex systems with fine magnetic proper-tiesPrincipal investigator: Peter Kopčanský

Project of Science and technology assistanceagency APVT:

APVT–20–009902 Low–dimensional magneticmaterials, Theme 8: Photo–magnetic andmagneto–optical materials based on analoguesof Prussian blue and nitropruside complexesCo–principal investigator: Marián Mihalik

APVT–20–018402 Synthesis and characteri-zation of nanomaterials prepared by non–traditional methods from metal–based materi-als precursors

Co–principal Investigator: Ivan Škorvánek

APVT–20–018402 Novel multiphase materialswith defined structure and extraordinaryphysical propertiesCo–principal Investigator: Ivan Škorvánek

STATE ORDER OF RESEARCH SO 51/03R 06 00/03R 06 03 - part 04 The devel-opment of materials by using of the mineralbiotechnbology, mechanochemical and chemicalroutesPrincipal investigator: Milan TimkoCo-principal Investigator: Ivan Škorvánek

Center of excelence:

NANOSMART Center of excellence for nanostruc-tured materialsCo–principal Investigators: Ivan Škorvánek,Pavel Diko

International projects:

Volkswagen Foundation VW–I/75961 SoftMagnetic Nanocrystalline Materials with Im-proved Combination of Application OrientedPropertiesPrincipal investigator: Ivan Škorvánek

COST 523 (EU–action) Soft Magnetic Struc-tural and functional properties of soft magneticnanocrystalline materialsPrincipal investigator: Ivan Škorvánek

S&T Cooperation between Slovakia andChina (project 2–3–8)Structure and properties of magnetic metalnanocapsulesPrincipal investigator: Ivan Škorvánek

NATO PST.EAP.CLG 981072 Novel soft mag-netic alloys with high critical temperaturesPrincipal Investigator: Ivan Škorvánek

CRNS 11911 French–Slovak project SoftMagnetic Study of magnetic properties inHITPERM–type nanocrystalline alloysPrincipal investigator: Ivan Škorvánek

SCENET–2, The European Network for Su-perconductivityFunded by the European Commission withinthe framework of the GROWTH programme ofthe 5th framework programmePrincipal investigator: Pavel Diko

DEPARTMENT MAGNETISM 9

EFFORT, The European Forum for Proces-sors of Large Grain (RE)BCOFunded by the UK gowernment and by Euro-pean CommissionPrincipal investigator: Pavel Diko

Slovakia – Spain project No. 07/2001Subgrain structure and properties of YBCOhigh Tc superconductorsPrincipal investigator: Pavel Diko

NATO SCIENCE PROGRAMME, CooperativeScience and Technology Sub-Programme,COLLABORATIVE LINKAGE GRANT No:PST.GLG.97876 (2002-2004), (IEP SAV, Ox-ford University, University of Michigan)Growth and Characterisation of ThalliumBased Superconducting Epi-layer FilmsProject Coordinator from a Partner country:Pavel Diko

NATO Collaborative linkage grantApplications of magnetic fluids in medicinePrincipal investigator: Peter Kopčanský

GROWTH research programme in frame of5FP EU New biocompatible nanoparticle de-livery system for targeted release of fibrinolyticdrugsPrincipal investigator: Milan Timko

Project No. 174/100 Slovak–Czechscientific–technical collaborationApplication of magnetic field in biomedicinePrincipal investigator: Peter Kopčanský

1.3 RESULTS

1.3.1 Cooperative phenomena in com-pounds containing f–element

The project is devoted to the study of coopera-tive phenomena in selected systems containing 4f-or 5f- metals in order to contribute to understandingof such phenomena as heavy–fermion behavior, spinfluctuations and long–distance magnetic ordering.The basic assumption of our success is crystal growthof high quality single crystals based on intermetalliccompounds of 4f- and 5f- metals and preparation ofsingle–phase molecular magnets based on Prussianblue analogues. We study crystal structure, mag-netic, electronic and transport properties of abovementioned systems. We focus to the study of ma-nifestations of itinerant and localized magnetism inthese materials. An attention is paid to the study ofmagnetic excitations, magnetic structures and crys-tal field schemes.

Structure, magnetic, transport and electronproperties of selected 4f- and 5f- intermetalliccompounds

Recent studies of the crystal and magnetic structureof U3M2M’3 compounds with M = Al, Ga and M’= Si, Ge revealed that all compounds crystallize ina new tetragonal structure of the U3Ga2Ge3 type,with space group I4, which is a low-symmetry deriva-tive of the Cr5B3 anti–type (space group I4/mcm).All compounds undergo a ferromagnetic transitionin the temperature range from 36 K to 90 K. A po-larized neutron study of the U3Al2Si3 single crys-tal showed that local anisotropy of the U3 ion leadsto the non–collinearity in the magnetic structure.For proper derivation of the uranium ground–statefrom low temperature specific heat measurements onU3M2M’3 materials, however, comparison with non-magnetic isotypes would be of benefit. No ternarycompound Th3M2M’3, where M = Al, Ga; M’ =Si, Ge, was observed with the U3Ga2Ge3 type ofcrystal structure [1]. In all cases the major phasecorresponded to solid solution of the M–metal com-ponent in binary ThSi2−y or ThGe2−y, respectively.The systematic inspection of the (U1−xThx)3Al2M3system, where M = Si, Ge and 0.00 ≤ x ≤ 0.25, re-vealed that the substitution of U with Th leads to anearly linear increase of the lattice parameters andthe U3Ga2Ge3 type of crystal structure, with spacegroup I4, is preserved up to the highest concentra-tion of Th. Magnetization measurements revealedthat the increase of the unit cell volume is followedby linear decrease of the Curie temperature from Tc= 64 K to Tc = 26 K in the case of the Ge–containingsamples and from Tc = 33 K to Tc = 26 K in the caseof the Si–containing samples. The saturated magne-tization µs is reduced by the U/Th–substitution forGe–samples, but in the case of Si–samples it displaysa complex behavior [2].

Magnetism in uranium based compounds is con-trolled by the degree of hybridization of U electronstates. In the crossover region between the strongand the weak hybridization limit often a heavy- -fermion, non–Fermi liquid behavior, and complexmagnetic ordering with reduced moments are ob-served. UIrGe belongs to compounds in which hy-bridization plays a very important role and in whichstrongly reduced U magnetic moments are expected.Although all the bulk properties of UIrGe pointto an antiferromagnetic (AF) ordering below 16–18 K, several neutron diffraction experiments failedto solve the magnetic structure of this compound.Neutron diffraction at low temperatures on a newlygrown UIrGe single crystal revealed a weak mag-netic signal on top of very few nuclear reflections.Refinements to models allowed by symmetry show


that a commensurate, non–collinear antiferromag-netic structure exists in UIrGe. U magnetic mo-ments are strongly reduced and amount at 1.8 K to0.36(8) µB [3].

The hexagonal compound UPdSn has attractedsubstantial attention in the past decade since theuranium 5f electrons exhibit a more localized char-acter, which is rather unusual among uranium in-termetallics. The magnetic properties of UPdSnare highly anisotropic with the c–axis as the hardmagnetization direction. Neutron diffraction estab-lished a complex non–collinear antiferromagnetic ar-rangement of U magnetic moments within the b–cplane below 40 K, followed by a second antiferromag-netic transition at about 25 K, where additional x–component to the moments were found. Both mag-netic phases are of orthorhombic symmetry. Themagnetic phase diagram of UPdSn for fields appliedalong the c–axis has been determined by means ofmagnetoresistance and neutron diffraction studies.We established that the 13 T c–axis transition isconnected with the 25 K zero–field transition, be-low which additional x -components to the magneticmoments are found [4]. Results of electrical re-sistivity measurements for a UPdSn single crystalat various temperatures, magnetic field and hydro-static pressures are presented in [5, 6]. Large magne-toresistance effects are observed in antiferromagnetic(AF) state, but also at temperatures far above TN ,which is attributed to existance of AF correlationsor short–range AF ordering in paramagnetic state.The value of TN is found increasing with increasingapplied hydrostatic pressure whereas T1, the tran-sition temperature from AF1 phase to AF2 phase,simultaneously decreases.

The study of the magnetic properties of ternary in-termetallic compounds of rare earth with iron, cobaltor nickel as a transition element is at present a top-ical field in the physics of materials both for thetechnological aspect related to the possible discov-ery of new permanent magnets and for the scien-tific interest connected with the presence of complexmagnetic behavior, i.e. spin reorientation transitionand first order magnetic transitions often observedin these phases. The RET4B compounds, where REis a rare earth, crystallize in the hexagonal CeCo4Bstructure, which can be derived from RENi5 by re-placing two Ni atoms at the 2c sites in every sec-ond layer by B atoms. In the CeCo4B structure theNi atoms occupy two kinds of crystallographic sites,(2c) and (6i), the rare earth element is also located intwo sites (1a), (1b) and boron occupies one position(2d). Recently, we have studied the magnetic prop-erties of RENi4B compounds with RE = Y, Ce, Pr,Nd, Sm, Gd, Tb, Dy, Ho and Er on polycrystalline

samples. YNi4B shows superconducting behaviourbelow 12 K, while CeNi4B and PrNi4B are param-agnets. All remained compounds are magneticallyordered with the ordering temperature ranging from6 K to 39 K. A large hysteresis loop is observed forthe SmNi4B compound with a coercive field Hc >7.0 T, whereas the RENi4B compounds of the otherrare earths are characterized by an Hc lower than0.06 T at 5 K. The large Hc value is indicative of asignificant anisotropy of this compound. The mag-netic moment µ of SmNi4B is equal to 0.32µB/f.u.at B = 9 T is reduced in comparison with the freeion value (m Sm = 0.71 µB)). X–ray photoemissionspectroscopy shows that the valence band is well sep-arated from the 4f peak. Between the Ni(2p(1/2))and Ni(2p(3/2)) peaks a satellite is visible, whichmay be related to the existence of a small magneticmoment on the Ni atoms [7, 8]. We have employedthe X–ray photoemission spectroscopy method tostudy the core levels of CeNi4X [9]. The analysisof the Ce(3d) peaks in the framework of the Gun-narsson and Schönhammer model provides informa-tion on the localization degree. The hybridizationparameter ∆ ≈ 85, 37 and 64 meV is found forCeNi4B, CeNi4Al and CeNi4Ga, respectively. Thesecompounds are of special interest due to the nearlyfilled Ni(3d) band implying a negligible contributionof Ni atoms to the resultant magnetic moment. Inthe temperature dependence of electrical resistivitywe have observed a shallow minimum for CeNi4X (X= Al, B, Ga) below 20 K. It has been ascribed to aKondo–like behavior [9]. The influence of mechani-cal alloying on the structural and physical propertiesof YNi4B and YNi4B intermetallic compounds werestudied in [10, 11].

RFe2Si2 compounds (R = rare earth metal) crys-tallize in the body–centered tetragonal crystal struc-ture of the ThCr2Si2–type with the space groupI4/mmm. This crystal structure is layered and of-ten exhibits a strongly anisotropic behavior. In thestructure the R, Fe and Si atoms occupy the 2a =(0 0 0), 4d = (0 1/2 1/4) and 4e = (0 0 z) crystallo-graphic sites, respectively. Iron ions carry no mag-netic moment, only the 4f electrons of rare earthatoms, which remain localized, carry magnetic mo-ments. The states of 5d and 6s electrons are inthe conduction band. The large 4f magnetic mo-ments can polarize the 5d electron states. In the pa-per [12] we report on the results of low-temperaturemagnetization, specific-heat and resistivity measure-ments on a TbFe2Si2 single crystal in magnetic fieldsup to 5 T applied parallel to the principal crys-tallographic axes. We conclude that TbFe2Si2 or-ders antiferromagnetically below TN = 5 K and ex-hibits strong uniaxial magnetocrystalline anisotropy.


Analysis of specific heat data has revealed a field-dependent Schottky contribution. The observed pro-nounced magnetocaloric effect points to a strongcompetition of the applied magnetic field and an-tiferromagnetic correlations in TbFe2Si2. Electronicstructure of TbFe2Si2 was studied by first principlescalculations in the framework of the density func-tional theory, which has confirmed the non-magneticcharacter of Fe sites [2]. Magnetic properties ofPrFe2Si2 and DyFe2Si2 single crystals have beeninvestigated using magnetization measurements inthe temperature range from 2 K to 300 K and inmagnetic fields up to B = 14 T. We have found astrong uniaxial anisotropy in the paramagnetic re-gion as well as in the magnetic order state withthe c−axis as an easy axis of magnetization in bothcompounds. The ordering temperature were deter-mined to be TN = 7.6 K and TN = 3.9 K andthe saturated magnetic moments µs = 2.46 µB/f.u.and µs = 10.27 µB/f.u. for PrFe2Si2 or DyFe2Si2,respectively. A metamagnetic transition at aboutBc = 0.5 T was found in magnetization measure-ments along the c−axis on both crystals. Theanisotropy of susceptibility and deviation from lineardependence of inverse susceptibility in the paramag-netic region are explained using a crystal field model[13].

In the papers [14, 15] we have investigatedthe magnetic structure of the fcc–antiferromagnetHoB12 and of some other dodecaborides by spe-cific heat and magnetization measurements, and byneutron diffraction. Specific heat and magnetiza-tion measurements up to 8 T show three magneticphases in the B vs T phase diagram. Powder neutrondiffraction in zero magnetic field reveals an antiferro-magnetic structure with basic reflections (0 2/3 2/3)and (2/3 1/3 2/3). In the magnetic phase at low-est field the principal reflections remain, in highermagnetic field they become suppressed. Moreover,the magnetic background strongly decreases with ap-plied field indicating that in zero field a part of themagnetic moments remains uncorrelated. Recentneutron diffraction investigations on a single crys-talline sample reveal an incommensurate amplitude-modulated magnetic structure of HoB12. The com-plex phase diagram of HoB12 can arise from theinterplay between the RKKY and dipole-dipole in-teraction, from the influence of the crystalline elec-tric field, and/or from frustration effects in the fcc–symmetry lattice. The received results are comparedwith the outcomes received on other magnetic dode-caborides and hexaborides.

Calorimetric tunneling spectroscopy

In the paper [16] we discuss basic principles ofa novel experimental technique, calorimetric tun-neling spectroscopy (CTS), based on precise mea-surements of the heat generated due to electrontunneling in vacuum barrier tunneling junctions(VBTJs). We argue that CTS represents an al-ternative/complementary experimental method tothe classical electron tunneling spectroscopy capa-ble to yield equivalent physical information. Carefulmeasurements of the current-voltage (I-V ) charac-teristics of tunneling junctions (TJs) can be usedfor the derivation of energy-spectroscopic informa-tion of solids. Many types of TJs, among themVBTJs and TJs with insulating barrier, were usedfor the determination of electronic densities of states(DOS) or inelastic excitation thresholds from mea-sured voltage dependence of dI/dV or d2I/dV 2, re-spectively. As well, measured d2I/dV 2 spectra ofsmall metal constrictions by means of point contact(PC) spectroscopy can contain structures which wellcorrelate with phonon spectra of studied metals andcan be related to the Eliashberg coupling functiong(ω) = α2F (ω). Unfortunately, PC spectroscopyworks well only in systems in which the dimension dof the contact is smaller than the mean free path lof electrons (d < l). This presents serious limitationfor a more wide utilization of the PC spectroscopy inthe modern solid state physics, where systems withvery short mean free path are frequently studied (e.g.heavy fermions or valence fluctuating systems). Thislimitation can be overcome if PCs operate in thetunnel regime. In our paper we conclude that CTScan be used for similar studies like ”classical” tun-neling spectroscopy based on measurements of I-Vcharacteristics. Thus its utilization can be found instudies of DOS, spin-polarized tunneling, Andreevreflection, EPI, etc. However, here should be notedthat CT experiments are not restricted only to stud-ies of energy-dependent processes by means of CTS,as described above, as they are capable to detect en-ergy processes separately in each TJ electrode andtherefore are sensitive to processes of energy radia-tion (e.g. light emission) from the volume of TJ aswell.

Structure, magnetic properties and heat ca-pacity of RE[Fe(CN)6].nH2O compounds

A substantial attention was paid to sample prepara-tion. Rare–earth ferricyanides RE[Fe(CN)6].4H2O(RE = Ce, Pr, Sm, Gd, Dy and Ho); Prussianblue analogues have been synthetized. The pow-der samples of RE[Fe(CN)6].nH2O were character-ized by means of IR spectroscopy thermal gravimet-


ric analyzes, NMR spectroscopy. Scanning electronmicroscopy was used to determine the distribution ofthe particles. The crystal structure of the rare–earthferricyanides was refined in according to hexagonalmodel (space group P 63/m, ICSD 2581). Whileaccuracy of the process for Pr[Fe(CN)6].5H2O sam-ple could be considered sufficient, the curves of dif-ference between calculated and measured patternsfor the other investigated compounds revealed dis-crepancies in x–ray intensities. The problem wassuccessfully solved by modification of the struc-tural model when the slightly modified model con-tains only four molecules of H2O per formula unit.The removal of the water molecule causes reduc-tion of the symmetry from hexagonal to orthorhom-bic (space group Cmcm, ICSD 203047) and the re-sult of the fitting procedure significantly improved[18]. In the paper [19] we present an analysis ofthe powder neutron diffraction patterns taken fromthe Dy[Fe(CN)6].4D2O at room temperature and inthe temperature range 1.6 - 40 K. Indexing pro-cedure has confirmed the orthorhombic symmetryof the phase Dy[Fe(CN)6].4D2O. The structureless(profile matching) fit gave refined values of latticeparameters a = 0.73629(3)nm, b = 1.27956(5)nm,c = 1.36087(5)nm. In accordance with the sin-gle crystal analysis of Pr[Fe(CN)6].4H2O for sym-metry description the Cmcm space group was sug-gested. Location of building units (FeC6 octahe-dra, D2O water molecules and other atoms thatwere taken as isolated) in the cell was performedby the direct–space method using reverse Monte–Carlo approach. The determined atom positionswere refined by Rietveld method combined with si-multaneous analysis of the neutron scattering den-sity distribution. The knowledge of the completecrystal structure, including the deuterium atomspositions, enables further investigation of magneticstructure of these types of materials from the neu-tron diffraction experiments. The investigated phasewas found to order magnetically bellow 2.8 K. Thediffraction patterns taken at temperatures 1.76 K -9.63 K show gradual development of magnetic mo-ment as temperature decreases [19]. Magnetiza-tion measurements on Ln[Fe(CN)6].nH2O crystals,where Ln = La, Pr, Sm and Dy revealed largeanisotropy between the easy and a hard magneticaxes. Transition to the magnetically ordered state isaccompanied by an anomaly in magnetization and alarge lambda anomaly in heat capacity with a max-imum at Tc = 1.3 K for Pr[Fe(CN)6].5H2O, Tc =3.5 K for Sm[Fe(CN)6].4H2O and Tc = 2.8 K forDy[Fe(CN)6].4H2O. Electron, phonon and magneticcontributions to heat capacity were determined forSm[Fe(CN)6].4H2O [20].

1.3.2 Photo–magnetic and magneto–optical materials based on ana-logues of Prussian blue and ni-tropruside complexes

For the last 15 years, there has been a great interestin the preparation of molecule–based magnets. Oneof the targets in the field of molecule–based magnetsis to prepare ferro- or ferrimagnets with high Curietemperatures (TC). The sample V[Cr(CN)6].7H2Ois amorphous, the sample (VO)3[Cr(CN)2]2.4H2Ois cubic, Fm3̄m space group with lattice parame-ter a = 1.0377(11) nm. M(T) dependence showsan increase of magnetization below the paramag-netic Curie temperature Tcp = 107 K and Tcp =167 K for the complexes with VIV and with VIII ,respectively. Both compounds are ordered ferrimag-netically below the Curie temperature TC = 53 K(VIV ) and TC = 88 K (VIII) determined by theWeiss method from M2 vs T dependence. Experi-mentally found µs = 0. 63 µB (VIV ) and µs = 0.91µB (VIII) corresponds well with the theoretical one.The irreversibility in FC and ZFC magnetization wasobserved. The maxima in M(T) at Tmax = 16 K(sample VIV ) and at Tmax = 32 K (sample VIII)at H = 10 Oe shift to lower temperatures and be-come less pronounced at higher magnetic fields. TheH–dependence Tmax and bifurcation Tirr suggests acluster glass behavior. Both samples exhibit a strongelectron paramagnetic resonance signal at g(VIII)= 1.84 and g(VIV ) = 1.79 with the peak to peaklinewidth ∆Hpp( VIII) = 73 Oe and ∆Hpp (VIV )= 944 Oe at room temperature. Magnetic relax-ation measurements for V[Cr(CN)6].7H2O point outto cluster–glass behavior at low temperatures. Ob-tained results display a logarithmic behavior of themagnetization versus time dependence above t =180s. The slow non–exponential relaxation of mag-netization below t = 180 s indicates non–equilibriumnature of ZFC and is a certain signature of glassinessof investigated compound [21 - 23].

Nitroprussides display very interesting photo-induced transitions to the long-lived metastablestates. An interesting light induced magnetic or-dering effect was found in Ni[Fe(CN)5NO].xH2O.The charge transfer from FeII to NO+ group, dueto irradiation by light of the wavelength 475 nm,induces two antiferromagnetically coupled spins onFeII and NO+. In our paper [24] we report on mag-netic properties and Mössbauer spectroscopy resultsof Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+ nitro-prussides in their freshly precipitated form. Sus-ceptibility data of freshly precipitated nitroprus-sides TM[Fe(CN)5NO].xH2O (TM = Mn, Fe, Co,Ni, Cu) follow very well modified Curie–Weiss law


down to T = 5 K indicating paramagnetic state;nitroprusside containing Zn is diamagnetic with asign of paramagnetic contribution. Deviation fromCurie–Weiss law and magnetization measurementson MnNP, FeNP and CoNP below T = 5 K can in-dicate ferrimagnetic ordering at low temperatures.A hysteresis behavior in ZFC and FC magnetisa-tion with the temperature of bifurcation Tb = 6 Kwas found for CoNP and FeNP. Mössbauer spectrataken at room temperature (besides FeNP) consistof a single symmetric quadrupole–split doublet withparameters δ and ∆ typical for FeII ions in octahe-dral sites. A more complicated spectrum of FeNP isa consequence of different Fe environments [24].

Magnetic properties of molecule-based magnetshave been of recent interest though their magnetictransition temperature Tc and saturation magnetiza-tion are relatively low. On the other hand, anotherobjective in molecule–based magnetism is to developnew types of functionalyzed magnets e.g. photomag-nets . Recently, magnetic properties of molecularmagnets built on Mo(CN)8 blocks have been studied.In the paper [25] we report on the magnetic proper-ties of Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and (VO)2+

octacyano–molybdates, respectively. The 1H NMRspectroscopic analysis and magnetization measure-ments were performed on TM2+2 [Mo

IV(CN)8].nH2Ocompounds (TM = Mn, Fe, Co, Ni, Cu, VO). The1H NMR signals reflect the magnetic moment of theTM ions (µP). The decay rates of FID signals in-crease as µP and the applied static rf field increase.The spin–lattice relaxation times at 27.7 MHz varyfrom 0.0187 ms (Mn) up to 0.45 ms (Cu). Magneti-zation measurements indicate ferrimagnetic orderingin Mn– and Co–compounds, and short range mag-netic ordering in Ni–compound. Susceptibility datafollows the Curie Weiss law above T = 20 K [25].

Recently, new molecular magnets based on[WV(CN)8]3− precursors have been synthesizedand characterized. The crystal structure con-sists of CuII4 [W

V(CN)8]3− anionic double layerswith tetrenH5+5 (tetren = tetraethylenepentamine)counter cations and water molecules located betweenthe sheets. Unit cell is orthorhombic, space groupCmc21 with unit cell parameter a = 0.7379 nm, b= 3.1725 nm and c = 0.7012 nm. The distancebetween the double-layers is about 1 nm. Mag-netic interactions between CuII (S=1/2) and WV

(S=1/2) ions are realized through cyanide bridgeand lead to the occurrence of ferromagnetic order-ing at transition temperature Tc = 34 K. Param-agnetic susceptibility follows the Curie–Weiss lawwith the positive θ = 44 K, C = 3 emu K mol−1

which corresponds to spin only value expectedfor an uncoupled spin system of 4 Cu spins and

4 W spins. Magnetization and AC-susceptibilitymeasurements performed under high pressure on(tetrenH5)0.8{CuII4 [WV(CN)8]4} x 7.2H2O com-pound revealed a pronounced decrease of the Curietemperature with a pressure coefficient dTc/dP =- 7.2 K/GPa. The identical value of dTc/dP hasbeen derived from M(T ), χAC(T ) and Arrot’s plotsmeasured under different pressures. Almost negli-gible effect of pressure on magnetization Ms pointsout to a localized character of magnetic moments inthe studied octacyanotungstate. The curve of theinitial magnetization changed its shape, remanentmagnetization Mr and coercive field Hc are reducedby applied pressure substantially [26].

A. Zentko, M. Zentková, J. Kováč, M. Miha-lik, Z. Mitróová, V. Kavečanský, M. Sendek,M. Lukáčová, M. Timko, I. Baťko, S. Maťaš,E. Bystrenová, K. Csach, J. MǐskufCollaboration in Slovakia:J. Briančin, J. Trpčevská (IMS SAS, Košice),J. Chomič (Faculty of Sciences, Universityof P.J. Šafárik, Košice), M. Miglierini, M. Se-beŕıni, A. Grusková (Slovak University ofTechnology, Bratislava)International collaboration:Z. Šimša, M. Maryško, J. Šebek, J. Ka-marád, Z. Arnold (Institute of Physics,Prague), V. Sechovský, P. Svoboda, M. Divǐs,L.Havela, A. Andrejev (Charles University,Prague), P. Stopka (IACH ASCR, Řeš),K. Prokeš (HMI, Berlin), G. Konczos,M. Bokor, L.F. Kiss (KFKI Budapest),M. Baran, R. Szymczak, H. Szymczak (IPPAS, Warsaw), R. Troc, W. Suski, K. Wo-chowski (ILTP PAS Wroclaw), T. Tolinski,A. Kowalczyk, A. Szlaferek (IMP PAS),M. Ba landa, T. Wasiutynski, (INP PASKrakow), B. Sieklucka (Jagiellonian Uni-versity, Krakow), F.P. Rogl (University ofVienna)

1. V. Kavečanský, P.Rogl, H. Noel, M. Mihalik,K. Wochowski, R. Troć: X-ray investigation ofalloys Th3M2M

′

3, M = Al, Ga, M′

= Si, Ge, J.Comp. and Alloys 365 173–177 (2004).

2. M. Mihalik, V. Kavečanský, K. Wochowski,R. Troć, P. Rogl: Magnetic properties of(U1−xThx)3Al2M3 compounds, Czech. J. Phys.54 D303–D305 (2004).

3. K. Prokeš, H. Nakotte, V. Sechovský, M. Miha-lik, A.V. Andreev: On the magnetic structureof UIrGe, Physica B 350 e199–e202 (2004).


4. H. Nakotte, S. Chang, A.M. Alsmadi, M. H.Jung, A.H. Lacerda, K. Prokes, E. Bruck,M. Mihalik: Hard-axis magnetoresistance andmetamagnetic transition in UPdSn Acta Phys-ica Polonica B 34 987–990 (2003).

5. F. Honda, A. Alsmadi, V. Sechovsky, J. Ka-marad, H. Nakotte, A.H. Lacerda, M. Miha-lik: Magnetoresistance of UPdSn and pressureeffect, Acta Physica Polonica B 341197–1200(2003).

6. F. Honda, A. Alsmadi, H. Nakotte, J. Kamarad,V. Sechovsky, A.H. Lacerda, M. Mihalik: Ef-fect of pressure on the electrical resistivity andmagnetism in UPdSn High Pressure Research23 177–180 (2003).

7. T. Tolinski, G. Chelkowska, B. Andrzejewski,A. Kowalczyk, M. Timko, J. Kováč: XPS andmagnetic studies of SmNi4B compound, Phys.Stat. Sol. (a) 196 294–296 (2003).

8. T. Tolinski, G. Chelkowska, B. Andrzejewski,A. Kowalczyk, M. Timko, J. Kováč: XPS andmagnetic studies of SmNi4B compound, Phys.Stat. Sol. (a) 196 294–296 (2003).

9. T. Tolinski, A. Kowalczyk, V. Ivanov, G.Chelkowska, M. Timko: Mixed–valence andKondo–like effect in CeNi4X (X = B, Al, Ga),Czech. J. Phys. 54 D287–D290 (2004).

10. M. Timko, A. Kowalczyk, A. Szlaferek, J.Kováč, A. Zentko, T Tolinski: The influenceof mechanical alloying on the structural andphysical properties of YNi4B intermettalic com-pound, , Phys. Stat. Sol. 196 201–204 (2003).

11. A. Szlaferek, A. Kowalczyk, B. Andrzejewski,M. Timko, J. Kováč, J. Briancin: Effect of me-chanical alloying on the structural and magneticproperties of DyNi4Al compounds, Czech. J.Phys. 54 D371–D374 (2004).

12. Matúš Mihalik, J. Vejpravová, J. Rusz, M.Divǐs, P. Svoboda, V. Sechovský, Marián Mi-halik: Anisotropic magnetic properties andspecific–heat study of a TbFe2Si2 single crystal,Phys. Rev. B 70 134405 (2004).

13. Matúš Mihalik, P. Svoboda, J. Rusz, V. Se-chovský, Marián Mihalik: Magnetic propertiesof selected RFe2Si2 compounds, Czech. J. Phys54 D283–D285 (2004).

14. S. Maťaš, I. Baťko, K. Flachbart, Y. Paderno,N. Shitsevalova, K. Siemensmeyer: Neutrondiffraction on HoB12, Journal of Magnetism andMagnetic Materials 272-276 e435-e437 (2004).

15. K. Siemensmeyer, S. Maťaš, M. Meissner, S.Gabáni, I. Baťko, K. Flachbart, A. Czopnik,Y. Paderno, N. Shitsevalova: Intricate magneticproperties of some rare earth dodecaborides,Czech. J. Phys 54 D273–D276 (2004).

16. I. Baťko, M. Baťková: Calorimetric tunnelingspectroscopy as a perspective tool for deriva-tion of energy-spectroscopic information in elec-trically conductive solids, Czech. J. Phys 54D619–D622 (2004).

17. K. Šterbaková, A. Zentková, A. Zentko: TheBarkhausen effect and the anomalous magneti-zation losses in metallic ferromagnets, Czech. J.Phys 54 D55–D58 (2004).

18. Z. Mitroóvá, A. Zentko, J. Trpčevská, M.Lukáčová, K. Csach, M. Bokor: Rare earth fer-ricyanides, Solid State Chemistry... 90-91 85–90 (2003).

19. V. Kavečanský, M. Mihalik, Z. Mitróová,M. Lukáčová, S. Maťaš: Neutron diffractionstudy of crystal and magnetic structure ofDy[Fe(CN)6].4D2O, Czech. J. Phys. 54 D571–D574 (2004).

20. Z. Mitróová, Marián Mihalik, A. Zentko, M.Lukáčová, Matúš Mihalik, J. Vejpravová, L.F.Kiss: Magnetic properties and heat capacity ofselected Ln[Fe(CN)6].nH2O compounds, Czech.J. Phys. 54 D559–D602 (2004).

21. A. Zentko, M. Bokor, M. Mihalik, Z. Mitróová,M. Lukáčová, M. Maryško, M. Zentková: Mag-netic properties of Pr[Fe(CN)6]5H2O, Phys.Stat. Sol. (a) 196 340–343 (2003).

22. M. Sendek, K. Csach,V. Kavečanský, M.Lukáčová, M. Maryško, Z. Mitróová, A. Zen-tko: Magnetic viscosity in vanadium chromi-cyanides, Phys. Stat. Sol. (a) 196 225–228(2003).

23. M. Lukáčová, L.F. Kiss, M. Maryško, MihalikM, Z. Mitróová, P. Stopka, Zentko A, M. Zen-tková: New magnetic phenomena in vanadiumhexacyanochromates, Phys. Stat. Sol. (a) 196240-243 (2003).

24. M. Zentková, M. Mihalik, I Tóth, Z. Mitróová,A. Zentko, Martin Sendek, J. Kováč, M.Lukáčová, M. Maryško, M. Miglierini: Mag-netic and Mössbauer study of some transitionmetal based nitroprussides, Journal of Mag-netism and Magnetic Materials 272-276 e753-e754 (2004).


25. M. Sendek, A. Zentko, M. Mihalik, M. Zen-tková, Z. Mitróová, V. Kavečanský, M. Bokor,M. Maryško: Magnetic properties and 1H NMRstudy of TM2+2 [Mo

IV(CN)8].nH2O, Czech. J.Phys 54 D551–D554 (2004).

26. M. Zentková, M. Mihalik, Z. Arnold, J. Ka-marád, M. Ba landa, R. Podgajny, B. Sieklucka:High pressure effect on ferromagnetic orderingin layered copper octacyanotungstate, Czech. J.Phys 54 D527–D530 (2004).

1.3.3 Magnetic nanoparticles andtheir role in different physicalsystems

Magnetizable complex systems for biomedi-cine

For the application of magnetic nanoparticles andmagnetic fluids in biomedicine is important to havebiocompatible systems with fully characterizationtheir magnetic properties, particle size and parti-cle size distribution for estimation quantity of im-mobilized biologically active substances and theirresponse on external magnetic fluids [1–6]. In or-der to improve the accumulation of magnetite par-ticles in target site the magnetoliposomes were de-veloped. This new type of vesicle consisted of nano-sized magnetic particles or magnetic fluid wrappedin a phospholipids bilayer with or without drugs of-fers new challenges in the field of modern biotech-nology and biomedicine. To overcome problem withreleasing of drug from the magnetoliposomes a va-riety of approaches have been employed includingcomplexation of DNA with cationic lipids, the de-sign of thermosensitive liposomes capable of releas-ing their contents in response to small changes intemperature, and the development of pH-sensitiveliposomes. We have used the magnetoliposomesconsisted of lipid mixture dipalmitoylphosphatidyl-choline (DPPC) with nanosized magnetic particlesand liposomes wrapped dye Crystal Violet for thestudy transmembrane transport [3]. The preparedmagnetoliposomes were observed using of Transmis-sion Electron Microscopy (Figure 2.1).

It was shown that there exists temperature de-pendent non-zero transport of dye from liposome tomagnetoliposome (Figure 2.2).

The lipid bilayer of the used DPPC provides asimplified model of cellular membrane because any”impurities” in the form of proteins are missing inthe lipid bilayer.

A new method for the determination of the sizedistribution of magnetic carrier systems, as wellas for the proof of successful immobilization of

Figure 1.1: The magnetite - coating liposomes withaverage diameter of 60nm.

Figure 1.2: Transfer of water soluble dye CrystalViolet from DPPC liposome to magnetoliposomesat room temperature and T=42 oC.

biomolecules to magnetic particles was developedand tested. The method is based on the ForcedRayleigh Scattering (FRS) experiment, in which adiffraction concentration grating is created in a thinsample of colloidal fluid due to the absorption ofan optical interference field. Using the FRS exper-iment the successful immobilization of dextran tomagnetic particles stabilized by sodium oleate wasproved (Figure 2.3).

The found mean hydrodynamic diameters ofsodium oleate stabilized magnetic particles beforeand after dextran immobilization were 27.02 nm and39.29 nm, respectively [15]. The increase of mea-sured diameters indicates the presence of bound dex-tran molecules. The found results show, that theForced Rayleigh Scattering can be successfully usedfor the determination of the size distribution of col-loidal magnetic particles in magnetic fluids and thus


20 40

0.0

0.2

0.4

0.6

0.8

1.0

1.2 magnetic particles + sodium oleate magnetic particles + sodium oleate + dextran

dH

dH

mean = 39.29 nm

mean = 27.02 nm

1201008060

dH [nm]

p (d

H)

Figure 1.3: The particle size distributions of sodiumoleate stabilized magnetic particles before and afterdextran immobilization..

for the detection of the increased hydrodynamic di-ameter of magnetic particles after successful immo-bilization of biomolecules, for example.

DC Dielectric Breakdown Strength in Mag-netic Fluids

We have studied the effect of an external magneticfield and magnetite particles concentration upon theDC dielectric breakdown strength in magnetic flu-ids [7–10]. The aim of this work was to verify theimprovement of dielectric properties for DC volt-age (not impulse DC voltage). Magnetic fluids usedin our experiments consisted of magnetite particles,coated with oleic acid as a surfactant, dispersed intransformer oil TECHNOL US 40005 (�r=2.1). Thevolume concentrations of magnetic particles were inthe range Φ=0.0025-0.02, the corresponding satu-ration magnetizations were in interval Is=1-8 mT.The mean diameter of magnetic particles Dv=8.6nm and standard deviation σ = 0.15 were obtainedby VSM magnetization measurements. The studyof the structuralization effect in magnetic fluids didnot show the presence of the needle like aggregationin magnetic fields up to 50 mT, unlike [7]. No os-cillations of the dielectric breakdown strength wereobserved, what proves, that the oscillations observedin [7] were caused by the presence of the needle likestructures. Figures 2.3 and 2.4 illustrate the depen-dencies of the DC dielectric breakdown strength onthe distance between the electrodes at two valuesof the saturation magnetization and various orienta-tions of external magnetic field. In both fluids theDC dielectric breakdown strength reaches its high-est values at the H ⊥E orientation. The dielectricproperties of magnetic fluid with Φ = 0.0025 andIs=1mT are better than those of the transformer oil

(Figure 2.4).

Figure 1.4: Dielectric breakdown strength vs. dis-tance between the electrodes for magnetic fluid (Φ=0.0025, Is=1 mT), transformer oil and oleic acid.

In magnetic fluid with Φ = 0.02 and Is=8 mTthese properties are worse compared with pure trans-former oil, besides of the regions with d < 0.2mmand d > 0.7mm, where the curves for magnetic fluidintersect the curve for Technol (Figure 2.5).

Figure 1.5: The same as in Figure 2.4 for Φ=0.02,Is=8mT.

The crossover from better to worse dielectric prop-erties was found to appear in magnetic fluid withIs=4 mT, approximately. To conclude it can be saidthat the field induced aggregation of magnetic par-ticles can significantly change the dielectric break-down strength of magnetic fluids if the sizes of theaggregates are comparable with the distance be-tween the electrodes of the measured gap. The in-vestigation of the dielectric breakdown in magneticfluids based on transformer oil TECHNOL US 4000confirmed the theoretically predicted decrease of thedielectric breakdown strength with increasing dis-tance between the electrodes in H=0 and H ⊥E. Inmagnetic field H ‖ E the magnetic particles aggre-gation led to the formation of the bridge across thegap between the electrodes, what lowered the dielec-tric breakdown threshold. It was showed, that stud-ied magnetic fluids, if their volume concentration ofmagnetic particles Φ


dielectric properties than pure transformer oil. Toconclude it can be said, that magnetic fluids withIs < 4 mT have better dielectric properties thanpure transformer oil and they are suitable for theuse as a high-voltage insulation.

The structural transitions in ferronematics

The electric Fredericksz transition [11–15]in 8CB liq-uid crystal-based ferronematics exposed to strongmagnetic field was studied both theoretically (bymeans of the Burylov and Raikher’s theory) and ex-perimentally (using capacity measurements) at dif-ferent volume concentrations of magnetic particles(f =5.10−4; 8.10−4; 1.10−3 and 2.10−3, respectively)[11–12]. The influence of external magnetic fieldand particle volume concentration on the capacitydependencies are shown on Figures 2.6 and 2.7, re-spectively.

Figure 1.6: The capacity vs. voltage dependenciesof the samples with different volume concentrationsf at B=4 T.

Figure 1.7: The capacity vs. voltage dependencies ofa sample with f=5.10−4 at different magnetic fieldsB.

The results of our measurements confirmed thetheoretically predicted decrease of the critical volt-age with particle volume concentration, as well asits increase with magnetic field growth. The valuesof the surface density of anchoring energy W andparameter ω = Wd/K≤1 ( d - typical size of mag-netic particle, K - Frank orientation-elastic modulusof liquid crystal). The finite value of W, as wellas the parameter ω characterize the soft anchoringof the nematic molecules on the magnetic particlessurfaces. The obtained values for the surface den-sity of anchoring energy and parameter ω felt intothe range W=(3.8 - 22.81).10-4 N/m and ω=0.73 -3.86, respectively. These quantitative values indi-cate some intermediate state between soft and rigidanchoring of liquid crystal molecules on magneticparticles surfaces in studied ferronematic exposed tostrong magnetic field.

P. Kopčanský, M. Koneracká, M. Timko,I. Potočová, N. TomašovičováCollaboration in Slovakia:A. Ziegelhofler (Institute For Research ofHeart, SAS, Bratislava)International collaboration:I. Šafař́ık (Institute of Landscape Ecol-ogy, Czech Academy of Sciences, ČeskéBudejovice), J. Jadzyn (Institute of Molec-ular Physics, Polish Academy of Sciences,Poznan, Poland), M. Trevan (Universityof Westminster, London, UK),G. Bossis(LPMC, University of Nice, Nice, France),L. Vekas (Centre for Fundamental andAdvanced Technical Research, RomanianAcademy of Science, Timisoara, Romania),P.C. Fanin (Trinity College, Dublin, Ireland),E. Chiellini (University of Pisa, Pisa, Italy)

1. M. Koneracká, P. Kopčanský, P. Sosa, J.Bagělová and M. Timko: Interlipoposomaltransfer of Crystal Violet dye from DPPC li-posomes to magnetoliposomes, accepted forJournal of Magnetism and Magnetic Materials,(2004).

2. M. Timko, M. Koneracká, P. Kopčanský, C.N.Ramchand, L. Vékas, D. Bica: Application ofmagnetizable complex systems in biomedicine.Czech. J. Phys. 54 D599–606 (2004).

3. A. Skumiel, A. Józefczak, M. Timko, P.Kopčanský, M. Koneracká: The effect of a mag-netic field on the absorption coefficient of ultra-sonic wave in biocompatible ferrofluid. Czech.J. Phys. 54 D651–654 (2004).


4. M. Timko, M. Koneracká, P. Kopčanský, Z.Tomori, L. Vékas, A. Józefczak, A. Skumiel,A. Radenovic, G. Dietler, E. Bystrenová, M.Lita: Complex characterization of physiologysolution based magnetic fluid. Indian Journalof Engineering and Materials Sciences 11 276–282 (2004).

5. M. Koneracká, P. Kopčanský, M. Timko, C.N.Ramchand, Z.M. Saiyed, M. Trevan, A. De Se-queira: Immobilization of enzymes on magneticparticles. Ed: J.M. Guisan (in press - Immobi-lization of Enzymes and Cells).

6. P. Kopčanský, M. Timko, I. Potočová, M.Koneracká, A. Juŕıková, N. Tomašovičová, J.Štelina, C. Musil, J. Bracińık: The determina-tion of the hydrodynamic diameter of magneticparticles using FRS experiment. accepted forJournal of Magnetism and Magnetic Materials(2004).

7. P. Kopčanský, L. Tomčo, K. Marton, M. Koner-acká, I. Potočová, M. Timko: Dielectric break-down strength in magnetic fluids. Phys. Stat.Sol. (b) 236 454–457 (2003).

8. P. Kopčanský, M. Koneracká, M. Timko, I.Potočová, K. Marton, L. Tomčo : The dielectricbreakdown strength of magnetic fluids based ontransformer oil. Czech. J. Phys. 54 D659–662(2004).

9. P. Kopčanský, L. Tomčo, K. Marton, M. Kon-eracká, I. Potočová, M. Timko. The experi-mental study of the DC dielectric breakdownstrength in magnetic fluids. Journal of Mag-netism and Magnetic Materials 272–276 2377–237856 (2004).

10. P. Kopčanský, L. Tomčo, K. Marton, M. Koner-acká, M. Timko, I. Potočová: The DC dielectricbreakdown strength of magnetic fluids based ontransformer oil, accepted for Journal of Mag-netism and Magnetic Materials (2004).

11. P. Kopčanský, I. Potočová, M. Koneracká, M.Timko, J. Jadzyn, G. Czechowski, A.M.G.Janse: The structural instabilities of ferrone-matic based on liquid crystal with low negativemagnetic susceptibility. Phys. Stat. Sol. (b)236 450–453 (2003).

12. P. Kopčanský, I. Potočová, M. Timko, M.Koneracká, A.M.G. Jansen, J. Jadzyn, G.Czechowski: The structural transitions in fer-ronematics in combined electric and magneticfields. Journal of Magnetism and Magnetic Ma-terials. 272–276 2355–2356 (2004).

13. P. Kopčanský, I. Potočová, M. Koneracká,M. Timko, A.M.G. Jansen, J. Jadzyn, G.Czechowski: Structural transition in ther-motropic ferronematic. Indian Journal of En-gineering and Materials Sciences 11 271–275(2004).

14. P. Kopčanský, I. Potočová, M. Koneracká, M.Timko, J. Jadzyn, G. Czechowski, A.M.G.Jansen: The structural transitions in ther-motropic ferronematics. Prof. of SPIE - Int.Soc. Opt. Eng. 5565 263–269 (2004).

15. P. Kopčanský, I. Potočová, M. Koner-acká, M. Timko, A.M.G. Jansen, J. Jadzyn,G. Czechowski: The anchoring of nematicmolecules on magnetic particles in some typesof ferronematics. accepted for Journal of Mag-netism and Magnetic Materials (2004).

16. I. Turek, J. Štelina, C. Musil, J. Bracińık, P.Kopčanský, M. Timko, M. Hnatič, M. Repašn,I. Potočová, L. Vékas, D. Bica : Light-inducedstructuralization in magnetic fluids with nega-tive Soret constant. Czech. J. Phys. 54 D655–658 (2004).

17. R.P.Pant, S.K. Dhawan, D.K. Suri, M. Arora,S.K. Gupta, M. Koneracká, P. Kopčanský,M. Timko: Synthesis and characterization offerrofluid-conducting polymer composite. In-dian Journal of Engineering and Materials Sci-ences 11 267–270 (2004).

18. P. Kopčanský, M. Hnatič, M. Repašan, I.Potočová, M. Timko, I. Turek, J. Štelina, C.Musil, J. Bracińık, E. Ayrjanc, L. Vékas, D.Bica: The light induced structuralization inmagnetic fluids with negative Soret constant ac-cepted for Journal of Magnetism and MagneticMaterials (2004).

1.3.4 GROUP OF NANOSTRUC-TURED MAGNETIC MATE-RIALS

The research activity of the group during 2003-2004has been focused on both the fundamental and theapplied research in the field of nanostructured mag-netic materials. Of particular interest was to betterunderstand the composition-structure-property rela-tionships in various advanced nano-phased magneticmaterials, where the nano-sized building blocks arearranged into different topological order. The mainattention was devoted to the soft magnetic alloys inthe form of ribbons (either amorphous or nanocrys-talline) with bcc-Fe, Fe(Si) and FeCo nanoparticles


embedded in a residual amorphous matrix. The re-sults of these investigations were published in the pa-pers [1-3], [5-8], [10-11], [13-14],[16-22], [24-28]. Ourattention was oriented also to the magnetic char-acterization of new types of magnetic nanoparticlesand nanocapsules, which were prepared by arc dis-charge method in different gas atmospheres [4,9,15],by chemical way [30] or by mechanochemical route[ 12,23,29]. The most important scientific resultscan be summarized as follows: i) With regard tothe envisaged technological aspects, the interestingresults towards a deeper understanding of the mag-netic softness have been achieved on FeNbB-basedNANOPERM-type alloys. These materials clearlyrevealed the dominating influence of the exchangeinteraction between the Fe-nanocrystals on the re-duction of the average anisotropy and of the coer-cive field. The temperature variation of coercivefield, Hc(T), for the samples with different contentof nanocrystalline particles is depicted in Fig. 1.8.

Fig. 1 Temperature dependence of coercive field for nanocrystalline Fe

0 100 200 300 400 500 600 700 800 900

0

2000

4000

6000

8000 Fe80.5Nb

7B12.5

Coercivity [Am-1]

T [K]

470oC/1h

510oC/1h

610oC/1h

0 20 40 60 80100

10

100

Coercivity [Am-1 ]

T [K]

Figure 1.8: Temperature dependence of coercivefield for nanocrystalline Fe80.5Nb7B12.

Approaching the Curie-temperature Tc of theamorphous matrix from below, Hc(T) increased froma low value – presumably determined by residualstresses – by almost three orders of magnitude due tothe weakening of the exchange and the restoration ofthe crystalline anisotropy of the nanograins. AboveTc, superparamagnetic fluctuations reduce Hc(T),however, also the magnetization is decreased to lev-els which is not good for practical applications.

Along with the strong high–temperature harden-ing, we realized as an interesting feature a signif-icant increase of Hc(T) at very low temperatures.This observation was associated with the formationof a cluster spin-glass due to random anisotropiesresiding in the interfaces between nanocrystals andthe matrix, which also reduce the intergranular ex-change [3, 7, 8 ]. ii) By a systematic substitutionof iron by cobalt, which implies the transition from

Figure 1.9: High Resolution TEM micrographs ofGd/GdC2 nanocapsules (b) and Gd nanoparticles(c).

NANOPERM to a HITPERM-alloy, we could suc-cessively increase the Tc of the amorphous host andalso the spontaneous magnetization. The resultingincrease of the intergranular exchange maintainedthe low Hc(T) up to 500oC. Considering also the ab-sence of a low-temperature hardening, we associatedthis technically almost ideal behaviour with a reduc-tion of the random anisotropy in HITPERM. More-over, by annealing in a magnetic field, we achievedcoercive fields below 10 A/m, a record mark forHITPERM which, moreover, proved to be stable upto high temperatures [1,2,10,27]. iii) Gd nanopar-ticles and carbon coated Gd/GdC2 nanocapsuleshave been prepared by means of arc discharge inargon and methane, respectively [4]. This tech-nique has been used also for preparation of Dy basednanoparticles and nanocapsules [9] as well as of thenanoparicles of immiscible system Co20Cu80 [15] In


the Gd nanoparticles, gadolinium oxide was detectedby X-ray diffraction, while the presence of metal-lic gadolinium was proved by oxygen analysis andX-ray photoelectron spectra. In the nanocapsules,GdC2 and Gd were detected by X-ray diffraction.Core/shell structures were observed for either thenanoparticles (with diameters larger than 20 nm) orthe nanocapsules (see Fig. 1.9).

For the nanoparticles with diameter less than20 nm, no difference was observed between the sur-face and the central region, indicating a completeoxidation of those relatively small Gd nanoparticles.Compared with that of the bulk Gd, the values ofthe Curie temperature of both samples are markedlyreduced. The possibility of the existence of the spin-glass-like state is discussed for Gd nanoparticles andGd/GdC2 nanocapsules [4].

1. K. Pekala, J. Latuch, M. Pekala, I. Škorvánekand P. Jaskiewicz,Transport and magneticproperties of HITPERM alloys, Nanotechnol-ogy 14, 2003, 196–199.

2. I. Škorvánek, P. Švec, J. Marcin, J. Kováč,T. Krenický, M. Deanko, Nanocrystalline Cu–free HITPERM alloys with improved soft mag-netic properties, Physica Status Solidi (a) 196,2003, 217–220.

3. . Škorvánek, J. Kováč, J. Kötzler, Nanocrys-talline soft magnetic materials: Intergrain cou-pling and spin freezing effects, Physica StatusSolidi (b) 236, 2003, 303–309.

4. P.Z. Si, I. Škorvánek, J. Kováč, D.Y. Geng,X.G. Zhao, Z.D. Zhang Structure and mag-netic properties of Gd nanoparticles and carboncoated Gd/GdC2 nanocapsules, Journal of Ap-plied Physics 94, 2003, 6779.

5. J. Kováč, J. Bednarč́ık, P. Kollár, M. Konč,K.Polañski, The magnetic properties and struc-ture of Co70.3Fe4.7Si10B15 powder prepared byball milling, Physica Status Solidi (a) 196,2003, 209–212.

6. P. Kamasa, A. Buzin, M. Pyda, J. Kováč,A. Cziráki, A. Lovas, I. Bakonyi, Temperature–modulated thermal and magnetic analysis ofamorphous alloys around magnetic and struc-tural phase transitions, Journal of Magnetismand Magnetic Materials 257, 2003, 274–283.

7. I. Škorvánek, V. Wagner, A neutron depolariza-tion study of low temperature magnetic harden-ing in FeNbCrBCu nanocrystalline alloys, Ma-terials Science and Engineering A, 375-377,2004, 1133–1136.

8. I. Škorvánek, J. Kováč, J. Kötzler, Tempera-ture evolution of coercive field and thermal re-laxation effects in nanocrystalline FeNbB alloys,Journal of Magnetism and Magnetic Materials272-276, 2004, 1503–1505.

9. P.Z. Si, E. Brück, Z.D. Zhang, I. Škorvánek,J. Kováč, M. Zhang, Preparation and prop-erties of dysprosium nanocapsules coated withboron, carbon and dysprosium oxide, MaterialsResearch Bulletin 39, 2004, 1005–1012.

10. E. Jedryka, M. Wojcik, P. Švec, I. Škorvánek,Nanocrystallization of FeCoZrB alloys studiedby Co-59 nuclear magnetic resonance, AppliedPhysics Letters 85, 2004, 2884–2886.

11. B. Idzikowski, A. Szajek, J.-M. Greneche,J. Kováč, Nanogranular FexNi23−xB6 phaseformation during devitrification of nickel–richNi64Fe16Zr7B12Au1 amorphous alloy, AppliedPhysics Letters 85, 2004, 1392.

12. E. Godočiková, P. Baláž, E. Boldižárová,I. Škorvánek, J. Kováč, W. Choi,Mechanochemical reduction of lead sul-phide by elemental iron, Journal of MaterialsScience 39, 2004, 5353–5355.

13. E.E. Shalyguina, I. Škorvánek, P. Švec,V.V. Molokanov, V. A. Melnikov, In-verted surface hysteresis loops in heterogeneous(nanocrystalline/amorphous) Fe81Nb7B12 al-loys, Technical Physics Letters 30, 2004, 591–594.

14. K. Pekala, M. Pekala, I. Škorvánek,Electrical resistivity of nanocrystallineFe73.5Nb4.5Cr5Cu1B16 alloys, Journal ofNon-Crystalline Solids 374, 2004, 27–30.

15. Cai-yin You, Z.Q. Yang, Q.F. Yang,I. Škorvánek, J. Kováč, Z.J. Li, W. Liu,Z.D. Zhang, Structural and magnetic charac-terization of Co–Cu nanoparticles preparedby arc-discharge, European Physical Journal-Applied Physics, 28, 2004, 73–77.

16. E.E. Shalyguina, I. Škorvánek, P. Švec,V.A. Melnikov, N.M. Abrosimova, Invertednear–surface hysteresis loops in heterogeneous(nanocrystalline/amorphous) Fe81Nb7B12 al-loys, Journal of Experimental and TheoreticalPhysics 99, 2004, 544–551.

17. E. Fechová, P. Kollár, J. Fuzer, J. Kováč,P. Petrovič, V. Kavečanský, The influence ofthe long time milling on the structure and mag-netic properties of the Fe-Cu-Nb-Si-B powder,


Materials Science and Engineering B107, 2004155–160.

18. J. Bednarčik, J. Kováč, P. Kollár, S. Roth,P. Sovák, J. Balcerski, K. Polanski, T. Švec,Crystallization of CoFeSiB metallic glass in-duced by long-time ball milling, Journal of Non-Crystalline Solids, 337, 2004 42–47.

19. M. Miglierini, T. Kaňuch, T. Krenický,I. Škorvánek, Magnetic and Mssbauer stud-ies of Fe76Mo8Cu1B15 nanocrystalline alloy,Czechoslovak Journal of Physics, 54, 2004,Suppl. D, pp. 73–76.

20. A. Lovas, K. Bán, J. Kováč, B. Zagyi, Neweffects and interpretation of amorphous Curiepoint relaxation in FeNi-based metallic glasses,Czechoslovak Journal of Physics, 54, 2004,Suppl. D, pp. 89–92.

21. D. Olekšáková, J. Fuzer, P. Kollár, T. Švec,J. Kováč, J. Briančin, K. Polanski, Structureand magnetic properties of powder permalloyFe-Ni, Czechoslovak Journal of Physics, 54,2004, Suppl. D, pp. 93–96.

22. P. Vojtanik, R. Andrejco, R. Varga, J. Kováč,K. Csach, A. Lovas, Magnetic and struc-tural properties of amorphous Co-Cr-Si-B al-loys, Czechoslovak Journal of Physics, 54, 2004,Suppl. D, pp. 113–116.

23. P. Baláž, E. Godoč́ıková, A. Aláčová,I. Škorvánek, J. Kováč, J.Z. Jiang, Mag-netic properties of nanocrystalline pyrrhotiteprepared by high-energy milling, CzechoslovakJournal of Physics, 54, 2004, Suppl. D, pp.121–124.

24. A. Bárdos, A. Lovas, D. Janovszky, J. Kováč,L.K. Varga, The influence of thermal his-tory on the crystallization properties ofFe70.7C6.7P10.4B5Si1.1Mn0.1Cr2Mo2Ga2 bulkglasses, Czechoslovak Journal of Physics, 54,2004, Suppl. D, pp. 125–128.

25. K. Bán, A. Lovas, J. Kováč, Cryogenic effectsin the amorphous Curie temperature shift ofFe-based glassy alloys, Czechoslovak Journal ofPhysics, 54, 2004, Suppl. D, pp. 141–144.

26. M. Kovalaková, L. Novák, A. Lovas, J. Kováč,Study of influence of chromium admixtureon hydrogenation and dehydrogenation of FeBamorphous ribbons, Czechoslovak Journal ofPhysics, 54, 2004, Suppl. D, pp. 149–152.

27. T. Krenický, J. Marcin, I. Škorvánek, P. Švec,Magnetic properties of FeCoNbB nanocrys-talline alloys heat treated under longitudinalmagnetic field, Czechoslovak Journal of Physics,54, 2004, Suppl. D, pp. 185–188.

28. I. Škorvánek, J. Kováč, Magnetocaloric be-haviour in amorphous and nanocrystallineFeNbB soft magnetic alloys, Czechoslovak Jour-nal of Physics, 54, 2004, Suppl. D, pp. 189–192.

29. P. Baláž, A. Aláčová, E. Godoč́ıková, J. Kováč,I. Škorvánek, J.Z. Jiang, Study of magneticproperties of nano-powders prepared by pyrite–troilite transformation via high energy milling,Czechoslovak Journal of Physics, 54, 2004,Suppl. D, pp. 197–200.

30. M. Pekala, V. Drozd, J. Kováč,I. Škorvánek, Magnetic characterizationof La0.75−xGdxCa0.25MnO3 manganites,Czechoslovak Journal of Physics, 54, 2004,Suppl. D, pp. 415–418.

I. Škorvánek, J. Kováč, J. Marcin,T. Krenický, P. Kulik

Collaboration in Slovakia:Institute of Physics SAS, Bratislava, (P.Švec),UGT-SAS, Košice, (P. Balž), Slovak Univer-sity of Technology,Bratislava (M. Miglierini),Faculty of Sciences, University of P.J. Šafárik,Košice, (P. Kolr)

International collaboration:Forschugszentrum-Geesthacht, FRG,(R. Gerling), Univ. Hamburg, FRG,(J. Kötzler), IMR, Shenyang, China,(Z. D. Zhang), Inst. of Physics PAS, Warsaw,Poland (E. Jedryka, M. Wojcik), Univ. LeMans, France, (J.-M. Greneche), WarszawUniversity, Poland (M. Pekala), MIT, Cam-bridge, USA, (R.C. O‘Handley), IEP-TU,Vienna, Austria, (R. Grssinger, R. Sato-Turtelli), HUT, Espoo, Finland, (O. Heczko),(IFM-Poznan, Poland (B. Idzikowski),KFKI-Budapest (L.K. Varga, A. Lovas),USF Tampa, USA (S. Hariharan)

1.3.5 GROUP CERAMIC SUPER-CONDUCTORS AND NANO-MATERIALS

Our results on investigation of microstructure ofbulk superconductors were summarised an published


as one chapter in The Handbook of Superconductiv-ity [1]. Summarised results on cracking of REBCObulk superconductors were presented as invited talkat the European Conference of Applied Supercon-ductivity, Sanremo, Italy 2003 [2] and as TopicalReview in Superconductor Science Technology 2004[3]. In last two years our research activities were fo-cussed on the cracking of YBCO bulks during oxy-genation (figure 2.10) [4,8,11-13] and on the fracturetoughness improvement by Ag addition [14,16] (co-operation with IFW Dresden, IPHT Jena, AI Wi-enna), on the modification of solidification processesof YBCO bulks with additions of alloying elements(Figure 2.11) [5-7,9,10,15,17] and on the formationof nanoparticles in these systems (figure 2.12)(co-operation with Cambridge University and ICMABBarcelona) [18-21]. Thermal analysis study of themelting and solidification of Bi nanoparticles ob-tained by mechanical milling of Bi-Al2O3, Bi-MgOand Ni-SiO2 systems has shown very high under-cooling of Bi-nanoparticles at solidification (figure2.13) indicating homogenious nucleation of Bi crys-tals (cooperation with IGT SAS Kosice and ElU SAVBratislava).

Figure 1.10: Measured (m) and calculated (c) crackspacing in the oxygenated layer on the surface of theY123/211 bulk superconductor oxygenated at dif-ferent temperatures. Crack spacing was calculatedaccording to Toules’s model. c-MAC means macro-cracks parallel to the c-crystal direction, a/b-MACmeans macrocracks parallel to the a/b-plane.

In review paper [3] the results on the crackingphenomena in melt-grown 123 bulk superconductorsare summarized. The reasons for cracking in this

Figure 1.11: 2 Growth morphology of the Y123/211sample with 0.8 wt. % depleted U addition. Thelayers of Uranium rich solidified melt, mixture of 211and U-based particles (Ubp) and layer of 123 phasefree of particles perpendicular to the solidificationdirection (SD) are product of a new growth modecalled cyclic growth.

material are mechanical stresses, which arise in thesample during its fabrication. Two main sourcesof stresses appearing during fabrication were iden-tified: the different thermal expansion coefficientof 123 and 211 phases and the dependence of 123phase lattice parameters on the oxygen stoichiome-try. The formation mechanisms of three basic typesof cracks are characterized. The most typical area/b-microcracks, which are observed as dense linesparallel to the a/b plane, and their length does notexceed some 211 interparticle distances. The a/b-microcracks are formed at 211 particles due to tan-gential tensile stress developed around each 211 par-ticle during cooling from the crystallization tem-perature and during oxygen uptake. The secondand the third type of observed cracks are so-calleda/b- and c-macrocracks. They extend along largersample areas and are formed under the combinedinfluence of tensile stresses developed during sam-


Figure 1.12: . New PtRuMoAl based platelike par-ticles 200 nm in thickness formed in the Y123/211system.

ple oxygenation and stresses induced by 211 con-centration macroinhomogeneity. Some possibilitiesof suppression of cracking are considered. Accord-ing to our analysis it is possible to find oxygena-tion conditions under which the formation of thec-macrocracks or both c- and a/b-macrocracks issuppressed. Other possibilities of suppression ofcracking such as oxygenation under uniaxial pres-sure, sample bandage and sample impregnation arediscussed. We have shown [4] that oxygenationof the melt-grown YBa2Cu3O7/Y2BaCuO5 singlegrain superconductors is associated with the for-mation of macro-cracks parallel to the a/b-plane.The origin of these cracks is associated with ten-sile stress induced into the oxygenated surface layerdue the c-lattice parameter shortening. The criti-cal strain calculated according to Thoules’s modelfor the cracking of brittle films on an elastic sub-strate suggests that the macro-cracking starts muchearlier than the formation of the homogeneous layerof equilibrium oxygen content at the surface. It isshown [5]that a microscopic inhomogeneities in theY2BaCuO5 (Y 211) concentration in the growth sec-tors (GSs) of single-grain melt-grown Y Ba2Cu3O7(1 2 3) bulks are associated with the developmentof growth subsectors (GSSs), which are formed dueto the existence of macrosteps at the growth front.Formation of the c-GSS in the a-GS leads to lo-

Figure 1.13: DSC cooling records showing ex-tremely high shift of solidification temperature of Binanoparticles prepared by high energy mechanicalmilling of Bi-ceramic systems. Bi melting tempera-ture is 271.3 oC.

cal low Y211 concentration and on the other handformation of the a-GSS in the c-GS causes a localincrease in Y211 concentration. The anisotropy ofthe pushing-trapping phenomenon is responsible forobserved changes in Y211 concentration. It is alsoshown that the macrosteps at the growth front canbe created due to differences in the growth rate ofsubgrains. 0.25 wt.of Ru addition to Y123/211 melt-grown bulk causes total 211 particle pushing [6] bythe growth front and 211 free Y123 single crystal isformed. The size of the 211 free Y123 single crystalwe obtained was 9.3 x 9.3 x 4.5 mm3. Ru is notsolved in the Y123 phase and is concentrated at thegrowth front. The 211 particles are pushed until acomplex Al, Ru, Pt, Y, Ba, Cu, O phase starts toform. The formation of this phase is initialized byAl pollution from the Al2O3 substrate. A decreaseof Jc was observed for the sample free of 211 parti-cles compared to standard samples. This effect wasmore pronounced in low magnetic fields and could beexplained by the absence of 211 interface pinning.

The shape of single-grain bulk Y-Ba-Cu-O(YBCO) samples fabricated with and without Ca-doping by top seeded melt growth (TSMG) hasbeen investigated [7]. Standard bulk samplesof YBCO containing 0.1 wt.Pt and enriched by30 molY2BaCuO5 (Y-211) exhibit a tapered up-per surface, with a high point at the positionof the seed. Bulk TSMG samples fabricatedfrom Y1:975Ca0:025Ba2Cu3O7 precursor powderenriched by 30 molY-211, on the other hand, arecharacterised by a upper surface. We propose amechanism for the taper formation in standard bulkTSMG samples, based on the edge melt distribution(EMD) effect, which is associated with liquid trans-


port from the slower growing a-axis growth front tothe more rapidly growing c-axis growth front at theinterface between a- and c-growth sectors. Pressureconsequently induced by this difference in growthrates is relaxed by displacing the growing crystal up-wards to form a taper from the position of the seed.Y-211 particle pushing in standard samples preventsback flow of liquid to the diffusion layer in the vicin-ity of the growth front, which maintains this pressureduring the growth process. Y-211 particle pushing isless apparent in Ca-doped samples, which accountsfor the absence of a tapered geometry in the topsurface of this material.

The oxygenation process of the top seededmelt-grown (TSMG) single-grain YBa2Cu3O7/Y2BaCuO5 (123/211) bulk superconductors wasstudied by microstructure observations [8]. It isshown that the c-cracks in these bulks are formed inthe oxygenated orthorhombic layer along the a/b-macrocracks. The lattice contraction of the 123phase in a/b-plane induces tensile stresses in theoxygenated layer, which cannot be relaxed by twinboundary motion. The critical spacing of the c-macrocracks, l = 14 µm, at oxygenation temper-ature 380 oC, estimated using Thoules’s model, isin a good agreement with the c-macrocrack spac-ing measures on standard TSMG 123/211 single-grain samples. The microstructure of single-grain,melt processed YBa2Cu3O7/Y2BaCuO5 (Y-123/Y-211) samples (YBCO) containing varying amountsof depleted uranium (DU) and Pt have been studied[9]. Only partial refinement of the Y-211 particlesize was observed in Pt-free samples, which gener-ally contained both small and large Y-211 particles.Small Y-211 particles in these samples are pushedextensively in the c-growth sector (c-GS) and allY-211 particles (small and large) coarsen with thedistance from the seed and with increasing DU con-centration. Samples fabricated with Pt containedonly very fine Y-211 particles, which were generallypushed strongly in the c-GS. In this case the sizeof the Y-211 particles did not vary significantly withdistance from the seed. U- and U/Pt-containing sub-micron sized particles present in the melt processedYBCO microstructure of were not pushed during so-lidification, although their arrangement within thestructure of the sample was influenced clearly bythe growth process. So-called cyclic growth was ob-served in the c-GS at the highest DU concentration(0.8 wt. In these samples, this growth pattern is as-sociated with the pushing of U-containing particlesand with the consequent formation of a liquid phaserich in U and Y at the growth front. The cyclicgrowth mechanism was modified by the addition ofPt. Crystals of Y2Ba4UCuOx with Ba3YUOx phase

inclusions were observed to be present in the U/Y-rich melt.

The microstructure of single-grain, melt processedYBa2Cu3O7/Y2BaCuO5 (Y-123/Y-211) samples(YBCO) containing varying amounts of depleteduranium (DU) and Pt have been studied [10]. Onlypartial refinement of the Y-211 particle size was ob-served in Pt-free samples, which generally containedboth small and large Y-211 particles. Small Y-211particles in these samples are pushed extensively inthe c-growth sector (c-GS) and all Y-211 particles(small and large) coarsen with the distance from theseed and with increasing DU concentration. Sam-ples fabricated with Pt contained only very fine Y-211 particles, which were generally pushed stronglyin the c-GS. In this case the size of the Y-211 par-ticles did not vary significantly with distance fromthe seed. U- and U/Pt-containing sub-micron sizedparticles present in the melt processed YBCO mi-crostructure of were not pushed during solidification,although their arrangement within the structure ofthe sample was influenced clearly by the growth pro-cess. So-called cyclic growth was observed in the c-GS at the highest DU concentration (0.8 wt. In thesesamples, this growth pattern is associated with thepushing of U-containing particles and with the con-sequent formation of a liquid phase rich in U andY at the growth front. The cyclic growth mecha-nism was modified by the addition of Pt. Crystalsof Y2Ba4UCuOx with Ba3YUOx phase inclusionswere observed to be present in the U/Y-rich melt.

We have shown that the a/b- and c-macrocracksstarts to form on the sample surface at the initialstate of oxygenation [11]. Shortening of the c- and(a+b)/2-lattice parameters with increasing oxygenconcentration induces tensile stresses on oxygenatedsurface layer and causes its cracking. Accordingto our analysis it is possible to find oxygenationcondition for three basic resulting microstructures:microstructure free of a/b- and c-macrocracks, mi-crostricture with a/b-macrocracks and without c-macrocracks and microstructure with a/b- and c-macrocracks.

It is shown that the a/b- and c-macrocracks startsto form on the surface of YBCO bulk superconduc-tors at the initial stage of oxygenation. Shorten-ing of the Y123 c- and (a+b)/2-lattice parameterswith increasing oxygen concentration induces tensilestresses on oxygenated layer and causes its cracking[12].

The paper [13] deals with an approximate model ofthermal-induced stresses in an anisotropic particle-matrix system of one spherical particle embedded inthe in.nite matrix. Radial and tangential stressesoriginate during a cooling process as a consequence


of di.erent thermal expansion coe.cients of the ma-trix and the particle, shear stresses are not consid-ered. In case of the matrix tensile radial stress, acrack forms in the matrix around the particle of aradius greater than a critical value obtained by anenergy balance criterion of the matrix crack forma-tion. Due to the fact that a shape of the crack inthe anisotropic matrix around the anisotropic par-ticle cannot be easily mathematically described, amodel of the circular crack in an isotropic planeof the particle-matrix system of matrix and parti-cle tetragonal lattices, forming in the brittle matrix,and consequently the formula of the particle criti-cal radius, are presented. Material constants of theY2BaCuO5 (211)-YBa2Cu3O7 (123) particle-matrixsystem are applicated for the calculation of the ra-dial and tangential stresses acting in the 123 matrixand in the 211 particle and for the calculation ofthe 211 particle critical radius representing the ma-trix crack formation condition as illustrated by theobserved matrix crack pattern.

The maximum field Bo =16 T was trapped at 24K in the gap of a mini-magnet made of two cylindri-cal samples [14]. Bo on top of a single cylinder was12.5 T at 20 K and 9 T at 40 K. The YBa2Cu3O7based bulk material was prepared by the modifiedmelt crystallization process from Y123, Y200, (Pt)precursor with 12 wt.forming silver precipitates inthe as grown materials. A bandage of stainless steelcompensated the tensile stress during magnetization.The unfavorable influence of admixed Ag on the crit-ical current density jc was compensated by dopingwith Zn ions. The influence of the ratio of smalland large size YBa2Cu3Ox (Y123) starting pow-ders on the microstructure development in the sin-tered and melt-textured YBa2Cu3O7 / Y2BaCuO5(Y211) bulk superconductors with the CeO2 addi-tion was studied [15]. It was shown that Y211 lowconcentration regions in the microstructure of themelt-textured samples are formed due to the pres-ence of large multigrain particles and/or agglomer-ates of small 123 particles in the starting Y123 pow-der. Moreover, it was observed that large Y211 par-ticles in the melt-textured samples are nucleated onthe surface of large Y123 grains during the sinteringstage. It is suggested that the insufficient mixing ofthe powders with higher portion of small Y123 parti-cles causes that the CeO2 concentration in the sam-ple is more inhomogeneous. Consequently the Y211particles can locally grow during peritectic meltingand temperature dwell.

We have investigated the phase equilibria in(RE)BaCuO/Ag systems, the influence of Ag on theprocessing of (RE)BaCuO/Ag composites and theresulting properties. YBaCuO/Ag composites have

been grown by the modified melt crystallisation pro-cess with YBa2Cu3O7, Y2O3, Pt and Ag2O3 inthe precursor [16]. The improved strength of theYBaCuO/Ag composites compared with the conven-tional YBaCuO bulk material permitted us to mag-netise these materials to achieve trapped fields up to16 T (at 24 K)in the gap of a mini-magnet. The in-vestigation of the microstructure revealed a remark-able increase of the spacing between micro-cracksespecially of those perpendicular to a/b-plane when12 wt Ag was added. In the case of SmBaCuO/Agcomposites, Ag has strong influence on processingand causes interaction between Re123 seeds and thesample. We show the growth of single-grain Sm-BaCuO/Ag composites in air and discuss the in-fluence of post-annealing on increasing Tc and Jc.Furthermore, YBaCuO/Ag composites have beenshown to be appropriate material used as a solderto join large grains to large arrays or to ”repair”grain boundaries in arrays grown by a multiseedingtechnique.

A quantitative analysis of 211-particle distributionin a Y123/211 (YBa2Cu3O7/Y2BaCuO5) bulks pre-pared by a top seeding melt-growth process (TSMG)was focussed mainly on measurement of 211-particleconcentration and 211 particle size distribution [17].The sample for this study was prepared using tem-perature programme, which led to the sharp changesof 211-particle concentration in the sample. Theconcentration and 211 particle distribution was mea-sured by image processing on the set of micrographsprovided by optical and scanning electron micro-scope (SEM) from the identical place of the sam-ple. Also in the sample with very small 211 particles(mean particle size, d211 = 0.6 mm) the measure-ment on optical micrographs was comparable withthe measurement on the SEM micrographs. The de-pendence of 211-particle concentration on the dis-tance from the seed was measured by two differenttechniques of image processing: count size measure-ment and line profile analysis. It was shown thatthe line profile analysis on the pre-treated opticalmacrographs could be calibrated and used for 211-concentration measurement.

The microstructural characterisation of single-grain YBa2Cu3O7/Y2BaCuO5 (Y123/Y211) bulksuperconductors with complex alloying based on Uand Al was performed by optical and scanning elec-tron microscope with EDAX microanalysis. Obser-vation showed that new platelike hexagonal parti-cles of submicron thickness were formed in the Y123crystal, in addition to the 211 particles [18].

The microstructure characterisation of single-grain complex alloyed (Mn,Ni,V,W,Mo)YBa2Cu3O7/Y2BaCuO5 (Y123/Y211) bulk su-


perconductors grown by TSMG (Top Seeding MeltGrowth) process was studied. The samples showedthat new particles of nanosize thickness were formedin the Y123 crystal, in addition to the 211 particles[19].

1. P. Diko, Chapter C.1.4. Optical Microscopy,in book ”Handbook of Superconducting Mate-rials”, Ed. D Cardwell, University of Cam-bridge, UK; D Ginley, NREL, USA IOP pub-lishing (2003) ISBN: 075030898 2.

2. P. Diko, G. Krabbes, Cracks in TSMG REBCOsuperconductors and their elimination, EUCAS2003, 7th European Conference on Applied Su-perconductivity, 14-18 September 2003, Sor-rento, Napoli - Italy, invited talk.

3. P. Diko, Cracking in melt-grown RE-Ba-Cu-Osingle-grain bulk superconductors, Topical Re-viev in Supercond. Sci. Technol. 17 (2004)R45-R58.

4. P Diko and G Krabbes, Macro-cracking in melt-grown YBaCuO superconductor induced by sur-face oxygenation, Supercond. Sci. Technol. 16(2003) 90-93.

5. P. Diko, K. Zmorayová, X. Granados, F.Sandiumenge and X. Obradors, Growth re-lated Y2BaCuO5 particle concentration micro-inhomogeneity in the growth sectors of TSMGYBa2Cu3O7/Y2BaCuO5 bulk superconductorPhysica C 384 (2003) 125-129.

6. P. Diko, L. Shlych, G. Krabbes, Ru assisted to-tal 211 particle pushing inmelt-grown Y123 su-perconductors,Physica C 390 (2003) 143-150.

7. P. Diko, K. Zmorayova, N. Hari Babu, D.A.Cardwell, Shape change during solidification ofbulk, single grain Y-Ba-Cu-O sample fabricatedby top seeded melt growth, Physica C 398(2003) 1-7.

8. P. Diko, G. Krabbes, Formation of c-macrocracks during oxygenation of TSMGYBa2Cu3O7/ Y2BaCuO5 single-grain super-conductors, Physica C 399 (2003) 151-157.

9. P. Diko, K. Zmorayová, N Hari Babu, G.Krabbes, D A Cardwell, The influence of the ad-dition of depleted uranium on the particle push-ing in melt-processed, bulk Y-Ba-Cu-O. Super-cond. Sci. Technol. 16 (2003) 1-8.

10. P. Diko, K. Zmorayová, N. Hari Babu, G.Krabbes, D. A. Cardwell, The influence of the

addition of depleted uranium on particle push-ing in the melt-processed YBCO bulks. Super-cond. Sci. Technol. 17 (2004) 186-193.

11. P. Diko, Cracking in TSMG YBCO supercon-ductors, Acta Metallurgica Slovaca, 10, 2004,570 - 577.

12. P. Diko, Oxygenation induced cracking inYBCO bulk superconductors, CzechoslovakJournal of Physics, Vol. 54 (2004), Suppl. D,pp. 445-448.

13. L. Ceniga, P. Diko, Matrix crack formationin Y-Ba-Cu-O superconductor, Physica C 385(2003) 329-336.

14. G. Krabbes, G. Fuchs, P. Verges, P. Diko, G.Stover, S. Gruss, 16 T trapped fields in modifiedYbaCuO: materials aspects, Physica C 378-381(2002) 636-640.

15. S. Kračunovská, P. Diko, D. Litzkendorf, T.Habisreuther, W. Gawalek, The influence ofthe starting YBa2Cu3Ox powder on the mi-croastructure of melt-textured YBa2Cu3O7−x/Y2BaCuO5 bulks, Physica C 397 (2003)123-131.

16. G. Krabbes, P. Diko, C. Wende, Th. Hopfinger,G. Fuchs, (RE)BaCuO/Ag Composites: TheRole of Silver in Bulk Materials and Joins, Ts-inghua Sciennce and Technology ISSN 1007-0214 02/11 pp251-265 Vol. 8. No. 3 June 2003.

17. K. Zmorayová, P. Diko, M. Šefč́ıková, X.Obradors, F. Sandiumenge, X. Obradors, Os-cilation of Y2BaCuO5 particle concentracion inthe melt growth bulk superconductors, CrystalGrowth 270 (2004) 685-690.

18. K. Zmorayová, M. Šefč́ıková, P. Diko, H. Babu,D. Cardwell. The microstructural characterisa-tion of YBCO bulk supreconductors with de-pleted uranium addition. Acta MetallurgicaSlovaca 10, 2004, (892-894).

19. M. Šefč́ıková, K. Zmorayová, P. Diko, H. Babu,D. Cardwell: Microstructure characterisationof YBCO bulk superconductors with complexalloying, Acta Metallurgica Slovaca 10, 2004,(889-891).

20. M. Šefč́ıková, K. Zmorayová, P. Diko, H. Babu,D. Cardwell: Nanosized Pinning centers inYBCO bulk superconductors with complex al-loing, Czechoslovak Journal of Physics, Vol. 54(2004), Suppl. D, pp. 473-476.


21. K. Zmorayová, M. Šefč́ıková, P. Diko, H. Babu,D. Cardwell: New pinning centres in YBCObulk superconductors with depleted uraniumaddition, Czechoslovak Journal of Vol. 54(2004), Suppl. D, pp. 469-472.

1.4 OTHER ACTIVITIES

1.4.1 Invited lectures

1. I. Škorvánek: Soft magnetic nanocrystallineFe(Co)NbB alloys, Intergranular coupling ver-sus temperature NATO Advanced ResearchWorkshop, Properties and Application ofNanocrystalline Alloys from Amorphous Precu-sors, Budmerice, June 8–14, 2003.

2. I. Škorvánek: Cluster structure, thermodynam-ics of formation and properties of nanocrys-talline alloys from amorphous precursors Eu-ropean Academy of Sciences Annual Congresson Materials Science and Nanotechnology,NANOMAT, Brussels, October 22–24, 2003.

3. P. Diko, chairman Session 7 Superconductors,nanomaterials, composites and other modernmaterials, INTERNATIONAL SYMPOSIUMON METALLOGRAPHY, 28-30TH APRIL2004, Star Lesn, Poprad, Slovak Republic.

4. M. Timko, Magnetizable complex system inbiomedicine, 12th Czech and Slovak conferenceof magnetism CSMAG’04, Košice, July 12–152004.

1.4.2 Organization of scientific con-ferences

1. Department of Magnetism of Institute of Ex-perimental Physics SAS together with Facultyof Sciences P.J. Šafárik University organized the12th Czech and Slovak conference of magnetismCSMAG’04, which was held in Košice, July 12–15 2004.

2. P. Diko, K. Zmorayová, M. Šefč́ıková organi-sation of The European Forum for Processorsof Bulk Superconductors (EFFORT) Meeting,Star Lesn 10-12 September 2004.

3. P. Diko, K. Zmorayová, participation in organ-isation of the conference: Celoslovenská konfer-encia o nanovedách, nanotechnologiách a nano-materiáloch NANOSVED, 13. -14. September2004, Košice, Slovensko.

department of magnetism · tremal soft magnetic materials is possible to use the diﬀerential...

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