Superconductivity Group (Politecnico di Torino):Roberto Gerbaldo, Gianluca Ghigo,

Laura Gozzelino, Francesco LavianoEnrica Mezzetti, Bruno Minetti

in collaboration withPiotr Przyslupski, Andrei Tsarou, Andrzej Wisniewski

Polish Academy of Sciences, Institute of Physics, Al. Lotnikov 32/46, Warsawa 02-668 - Poland

MagnetoMagneto--OpticsOptics of of SpontaneousSpontaneous and and fieldfield--inducedinduced VorticesVortices in in twinnedtwinnedYBaYBa22CuCu33OO77--δδ/La/La11--xxSrSrxxMnOMnO33 bilayersbilayers

OutlineOutline• Magneto-optical technique – a very brief survey

• Magnetic Phase Diagram of the Manganite compound: different dopings examined (comparison between La and Nd

manganites)

• Interaction between Vortices and Magnetic Structuresin YBCO/LSMO bilayers: vortexvortex channelingchanneling and and

controlledcontrolled guidanceguidance

• Magnetic Imaging of Domain and Domain-walls inManganite films on twinned substrates

• Preliminary results on magneto-optical imaging of the magnetic pattern in Cobaltite crystals

MagnetoMagneto--opticaloptical techniquetechnique

The polarization plane of the light refracted by the ferrite is rotated by an angle (αF) proportional to the lenght of the light path into the medium and to the localmagnetization component along the light direction.

TheThe FaradayFaraday effecteffect – M. Faraday, Trans. Roy. Soc. 146 (1846) 1

F.Laviano, D. Botta, A. Chiodoni, R. Gerbaldo, G. Ghigo, L. Gozzelino, S. Zannellaand E. Mezzetti, Supercond. Sci. Technol., 16 (2003) 71

Superconductor/Superconductor/ManganiteManganite HeterostructuresHeterostructures

a ~ 0.386 nma ~ 0.386 nm

Atomic structureclose to a cubicperovskite

LaLa11--xxSrSrxxMnOMnO

a = 0.382 nma = 0.382 nmb = 0.388 nm b = 0.388 nm c = 1.168 nmc = 1.168 nm

YBaYBa22CuCu33OO77--δδ

Orthorombicstructure

TEM image of [LSMO x 8 u.c. /YBCO x 3 u.c.] superlattice

P. Przyslupski et al. J. Appl. Phys. 95 (2004) 2906.

GoodGood matchingmatching betweenbetween manganitemanganiteand and highhigh--TTcc cupratecuprate latticeslattices

high high qualityquality heterostructureheterostructure

ManganiteManganite film film magnetizationmagnetization stronglystrongly dependsdependson on StrontiumStrontium doping doping levellevel

MagneticMagnetic PhasePhase DiagramDiagram of of SrSr--dopeddoped ManganiteManganitecompundscompunds: LSMO: LSMO

YBCO YBCO thicknessthickness: 50 : 50 nmnmLSMO LSMO thicknessthickness: 100 : 100 nmnmgrowngrown byby multitargetmultitarget sputteringsputtering **

* P. * P. PrzyslupskiPrzyslupski etet al.al. IEEE IEEE Trans.Trans. ApplAppl. . SupercondSupercond.. 7 (1997) 21927 (1997) 2192

LaAlO3

LSMOYBCO

LaLa00.67.67SrSr0.330.33MnOMnO33FerromagneticFerromagnetic, , metallicmetallic phasephase withwithTTcuriecurie== 360 K360 K

A.P. Ramirez, J. Phys.: Condens. Matter 9 (1997) 8171–8199

ManganiteManganite film film magnetizationmagnetization stronglystrongly dependsdependson on StrontiumStrontium doping doping levellevel

MagneticMagnetic PhasePhase DiagramDiagram of of SrSr--dopeddoped ManganiteManganitecompundscompunds: LSMO: LSMO

YBCO YBCO thicknessthickness: 50 : 50 nmnmLSMO LSMO thicknessthickness: 100 : 100 nmnmgrowngrown byby multitargetmultitarget sputteringsputtering **

* P. * P. PrzyslupskiPrzyslupski etet al.al. IEEE IEEE Trans.Trans. ApplAppl. . SupercondSupercond.. 7 (1997) 21927 (1997) 2192

LaAlO3

LSMOYBCO

LaLa00.885.885SrSr0.1150.115MnOMnO33FerromagneticFerromagneticinsulatorinsulator phasephase withwithTTCurieCurie = 180 K= 180 K

A.P. Ramirez, J. Phys.: Condens. Matter 9 (1997) 8171–8199

MagneticMagnetic PhasePhase DiagramDiagram of of NdNd--dopeddoped ManganiteManganitecompundscompunds: NSMO: NSMO

ManganiteManganite film film magnetizationmagnetization stronglystrongly dependsdependson on NdNd doping doping levellevel

YBCO YBCO thicknessthickness: 50 : 50 nmnmNSMO NSMO thicknessthickness: 100 : 100 nmnmgrowngrown byby multitargetmultitarget sputteringsputtering **

* P. * P. PrzyslupskiPrzyslupski etet al.al. IEEE IEEE Trans.Trans. ApplAppl. . SupercondSupercond.. 7 (1997) 21927 (1997) 2192

LaAlO3

NSMOYBCO

For 0.5 Nd doping levelthe ground state at low

temperature isantiferromagnetic!

MagnetoMagneto--opticaloptical ImagingImaging ofof LaLa00.67.67SrSr0.330.33MnOMnO33on on twinnedtwinned LaAlOLaAlO33

300 300 µµmm

OpticalOptical imageimage

TwinnedTwinned structurestructurein LAOin LAO

T = 300 K 0 < H[110] < 500 Oe

MultiMulti--domaindomain magneticmagneticpattern in LSMOpattern in LSMO

300 300 µµmm

TriTri--crystalcrystalpointpoint

MagnetoMagneto--OpticsOptics

LLaaAAllOO33 TTwin win BBoundariesoundaries induce induce splittingsplitting of of ManganiteManganite MagneticMagnetic DomainsDomainsand and outout--ofof--planeplane DDomainomain--WWalls alls ((DWDW’’ss) are ) are presentpresent

DomainsDomains and and DomainDomain--wallswalls inin LaLa00.67.67SrSr0.330.33MnOMnO33on on twinnedtwinned LaAlOLaAlO33

200 µm 200 µm

T = 100 K 0 < H[110] < 500 Oe

MagneticMagnetic domaindomain pattern pattern isis stablestable forfor T < T < TTCurieCurie

Patterns obtained Patterns obtained bybysaturatingsaturating the the magnetizationmagnetization withwithanan inin--planeplane magneticmagneticfieldfield in the (110) in the (110) directiondirection

Out of Out of planeplanemagneticmagneticmomentsmoments(( DW, i.e. DW, i.e. BBzz ))

Out of Out of planeplanemagneticmagneticmomentsmoments(( DW, i.e. DW, i.e. BBzz ))

DomainsDomains withwith in in planeplane magnetizationmagnetization

““SpontaneousSpontaneous”” VortexVortex PhasePhase in in YBaYBa22CuCu33OO77--δδ/ / LaLa00.67.67SrSr0.330.33MnOMnO33 bilayerbilayer

T=4.2K

samplesample edge

edge

200 200 µµmm

mT

8

6

4

2

0

-2

T = 4.2 K µ0Ha = 0 mTZERO FIELD COOLING When cooling below YBCO Tc,

vortex-antivortex rows are spontaneously nucleated on

out-of-plane magnetic domain walls(DWs) and they stay pinned at the

DW locations

BBzz ((brigthbrigth DW) DW) ——

BBzz (dark DW) =(dark DW) =∆∆BBzz ~ ~ 2.5 2.5 mTmT(i.e. 0.6 vortices/µm2 inside DW)

F. Laviano, L. Gozzelino, E. Mezzetti, P. Przyslupski, A. Tsarou, A. Wisniewski,ApplAppl. . PhysPhys. . Lett.Lett. 86, 152501 (2005)86, 152501 (2005)

Vortex ChannellingVortex Channelling ininYBaYBa22CuCu33OO77--δδ/La/La00.67.67SrSr0.330.33MnOMnO33 bilayerbilayer

-1 0 1 2 3 4 5 6 7 8 mT

∆∆BBzz [([(µµ00HHa a = 3 = 3 mTmT) ) –– ((µµ00HHa a = 0 = 0 mTmT)])]

200 200 µµmm

0 20 40 60 80 100 120 1401.0

1.5

2.0

2.5

3.0

3.5

4.0

DW

DW∆Bz (m

T)

position (µm)

Flux quanta Flux quanta pile uppile up on on DWsDWs of the same of the same vorticityvorticity, increasing the , increasing the local flux density local flux density (brighter lines), or (brighter lines), or partially partially annihilateannihilate on on DWsDWs of opposite sign of opposite sign (darker lines).(darker lines).

Perpendicular vortex motionPerpendicular vortex motion to YBCO twinto YBCO twin--boundaries (magnetized by the boundaries (magnetized by the underlying locked underlying locked DWsDWs))

T = 4.2 K µ0H||z = 3 mT

DWsDWs perpendicular to the perpendicular to the vortex motion direction vortex motion direction always always slow downslow down the the vortex diffusion processvortex diffusion process

Vortex GuidanceVortex Guidance ininYBaYBa22CuCu33OO77--δδ/La/La00.67.67SrSr0.330.33MnOMnO33 bilayerbilayer

Parallel vortex motionParallel vortex motion to YBCO twinto YBCO twin--boundaries (magnetized by the underlying locked boundaries (magnetized by the underlying locked DWsDWs))

longitudinal TBs with respect to the Lorentz drag force

T = 4.2 K

flux diffusionflux diffusion is enhancedenhanced for vortices of the same polarization of DWsdepresseddepressed for vortices with opposite sign with respect to DWs guidance

vortices diffusing parallel to DWs are affected by a two-fold channeling phenomena

Controlled GuidanceControlled Guidance of the flux quanta movement and arrangement

towards vortex magnetic memoryF. Laviano et al. – Appl. Phys. Lett. 86, 152501 (2005)

ComparisonComparison withwith the the electrodynamicselectrodynamics ofofYBaYBa22CuCu33OO77--δδ/ Nd/ Nd00.5.5SrSr0.50.5MnOMnO33 bilayerbilayer

15.7 Oe T = 4.2 K 46.4 Oe

• None flux trapped on cooling

• TB’s act only as very good pinning defects

T = 4.2 K µ0Ha = 0 mTZERO FIELD COOLING

50 µm

MagnetoMagneto--OpticsOptics

when cooling below YBCO Tc in zero applied fieldzero applied field,vortexvortex--antivortexantivortex singularities are spontaneously nucleatedsingularities are spontaneously nucleated along

the out-of-plane magnetic domains

Lower vortex density is induced with Lower vortex density is induced with respect to respect to LaLa00.67.67SrSr0.330.33MnOMnO33

Bz (brigther domains) —Bz (darker domains) =

∆Bz ~ 0.6 mT(i.e. 0.15 vortices/µm2 along the domains)

TrappedTrapped VortexVortex DensityDensity

““SpontaneousSpontaneous”” VortexVortex PhasePhase in in YBaYBa22CuCu33OO77--dd/ / LaLa00.885.885SrSr0.1150.115MnOMnO33 bilayerbilayerOpticalOptical imageimage

MMagneticagnetic DDomainomainss affects the affects the VVortexortex MMotionotion: : longitudinallongitudinal and and transversaltransversal channellingchannelling occuroccur at at DWDW’’ss

VortexVortex ChannelingChanneling in in YBaYBa22CuCu33OO77--dd/ / LaLa00.885.885SrSr0.1150.115MnOMnO33 bilayerbilayer

20 µm

T = 4.2 K µ0H||z = 7.5 mTT = 4.2 K µ0H||z = 4.5 mT

Magneto-optical frame

50 µm

Interaction of Interaction of VorticesVortices and and MagneticMagnetic DomainsDomainsin in YBaYBa22CuCu33OO77--dd/ La/ La00.885.885SrSr0.1150.115MnOMnO33 bilayerbilayer

0 10 20 30 40 500

4

8

12

edgesample

α

TB's

B z (mT)

position (µm)

mT20

16

12

8

4

0

α

βγ 50 µm

MagMagneticnetic domaindomain influenceinfluence on on the critical state pattern: the flux gradient the critical state pattern: the flux gradient seems to be periodicseems to be periodicallyally modulatedmodulated with discontinuities at TBwith discontinuities at TB’’ss locartionslocartions

T = 4.2 K µ0H||z = 4.5 mT

0 10 20 30 40 500

4

8

12

edgesample γ

β

B z (mT)

position (µm)

the vortex guidance over an extend domain is isotropicthe vortex guidance over an extend domain is isotropicL. Gozzelino et al., Supercond. Scie. Technol., 19 (2006) S50

LocalLocal SupercurrentSupercurrent ImagingImaging in in YBaYBa22CuCu33OO77--dd/ / LaLa00.885.885SrSr0.1150.115MnOMnO33 bilayerbilayer

1011

A/m2

2.5

2.0

1.5

1.0

0.5

0JφJr50 µm

1011 A/m2

1.5

1.0

0.5

0

-0.5

-1.0

-1.5

““SpontaneousSpontaneous vortexvortex--phasephase”” inducesinduces supercurrentsupercurrent modulationsmodulations inside the inside the MeissnerMeissner state (state (S. Erdin, I.F. Lyuksyutov, V.L. Pokrovsky, and V.M. Vinokur, PRL88(2002)017001))

0 20 40 60 80-2.0-1.5-1.0-0.50.00.51.01.5

J r (1010

A/m

2 )

position(µm)

T = 4.2 K µ0H||z = 4.5 mT

MOI

InteractionInteraction betweenbetween YBCO and LSMOYBCO and LSMO

1011

A/m2

3.0

2.5

2.0

1.5

1.0

0.5

0|J | 50 µm

T = 4.2 K µ0H||z = 4.5 mT

Jc ~ 2.5·1011 A/m2

supercarrier density islocally modulated bythe magnetic domain-wall structure

0 3 6 9 12

2.2

2.4

2.6

2.8

3.0 |J| (1011 A

/m2)

position (µm)

Local |J| depletion in correspondence of DW’s

LocalLocal SupercurrentSupercurrentModulationsModulations

MOI∆Jc ~ 8%

DifferentDifferent MagnetizationMagnetization statesstates in the in the FerromagneticFerromagnetic InsulatorInsulator (FI) (FI) phasephase(Tcurie ~180 K, applied field at T~4K)

DomainsDomains and and DomainDomain--wallswalls ininLaLa00.885.885SrSr0.1150.115MnOMnO33 on on twinnedtwinned LaAlOLaAlO33

100 µmT = 3.8 K ∇H[111] ∼10kOe mm-1

180180°° BlochBloch WallsWalls of of manganitemanganite are are visiblevisible in in betweenbetween the the DWDW’’s s pinnedpinned at theat the twintwin--boundariesboundaries ((TBTB’’ss)), , the the roughnessroughness isis due due toto the the energyenergy minimizationminimization of the of the DWDW’’ss

5 µm

ConclusionsConclusions•• MagnetoMagneto--opticaloptical imagingimaging of of magneticmagnetic patternspatterns in in

manganitemanganite film film withwith differentdifferent dopingsdopings and and manganitemanganite/superconductor /superconductor heterostructuresheterostructures::

1.1. influenceinfluence of the of the substratesubstrate structurestructure

2.2. ““SpontaneousSpontaneous”” VortexVortex PhasePhase: : magneticmagnetic pattern pattern freezedfreezed in the in the superconductor superconductor

3.3. VortexVortex channelingchanneling --> > controlledcontrolled guidanceguidance of of vorticesvortices byby magneticmagneticdomainsdomains and and domaindomain--wallswalls

•• SupercurrentSupercurrent imagingimaging allowsallows observingobserving the the locallocalelectromagneticelectromagnetic couplingcoupling in the in the superconductingsuperconducting//magneticmagneticbilayersbilayers ((in in progressprogress……))• ImagingImaging the the DomainDomain WallWall dynamicsdynamics, , in in manganitemanganite filmsfilms

withwith TBTB’’ss, , revealsreveals the way the way toto engineerengineer the the locallocal coercitivitycoercitivityof the material of the material byby suitablesuitable defectsdefects and and magneticmagnetic fieldsfields

ThanksThanks forforyouryour

attentionattention!!!!!!