The 2012 World Congress on Advances in Civil, Environmental, and Materials Research (ACEM’ 12)Seoul, Korea, August 26-30, 2012

Effect of Cu Contents on the Structural, Electrical and Magnetic Properties of Mn-Ferrites

Zaib-un-Nisa1), Shahid Atiq1,2),*, Saadat A. Siddiqi1,3), Saira Riaz1) and Shahzad Naseem1)

1Centre of Excellence in Solid State Physics, University of the Punjab, Lahore-54590, Pakistan

3Interdisciplinary Research Centre in Biomedical Materials (IRCBM), COMSATS Institute of Information Technology, Defense Road, Off Raiwind Road, Lahore, Pakistan

2)Email: shahidatiqpasrur@yahoo.com

ABSTRACT

The effect of Cu content have been studied on Mn-ferrite system by preparing the CuxMn1-xFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) compositions using sol-gel auto-combustion technique. The structural, morphological, electrical and magnetic properties were determined by x-ray diffraction, scanning electron microscopy, high resistivity meter and vibrating sample magnetometer, respectively. Lattice constants and porosity were observed to increase with the doping of Cu contents attributed to the smaller size of ionic radii of Cu++ (0.70) substituting the Mn++ (0.91) sites in structure. Morphological studies revealed the decrease in crystallite size with increasing the Cu contents. The electrical resistivity shows an increasing trend with the increase of Cu content. The magnetization of the samples first increase up to x = 0.4 in the series and then decreased with further increment of Cu contents. The results obtained for Cu0.4Mn0.6Fe2O4 emerged optimum, as having good combination of electrical and magnetic properties, for the consideration of this material at high frequencies, for their versatile applicability.

1. INTRODUCTION

Magnetic ceramics can be considered suitable materials for recording head applications because of their unique advantage over metallic materials due to their stability and wear properties (Valenzuela 2005). Ceramics are extremely hard and resistive to wear due to combination of ionic and covalent bonding. These are oxides, chemically stable and no further oxidation is normally, permissible. Magnetic materials are playing important role in numerous products around us, but the electrical resistivity of ferrites being millions times than metals have compactified their applications, particularly at high frequencies (Martirosyan 2002).

The polycrystalline ferrites envisage their extra ordinary importance, because of their adequate use as magnetic materials having high electrical resistivity, low eddy currents and dielectric loss. The speedily emerging interest in these ferrites is amid at their versatile applicability in telecommunication, audio and video, power transformers and

many other applications involving electrical signals, normally not exceeding a few megacycles per second (Wang 2008) The crystallographic, electrical and magnetic properties depend strongly not only upon the stoichiometry but also on various heat treatment steps, accorded during the course of preparation for the passable control of the corresponding microstructure (Ramay 2011).

Several techniques including solid state reaction, co-precipitation, micro emulsion and ball-milling (Patil 2002, Ahmed 2002, Rana 2003, Gajbhiye 2002) have been utilized to synthesize ferrites at micro and nano levels, which facilitate an ample opportunity to produce fine powders. But so-gel combustion being a novel, energy-efficient and simple method which contains a combination of chemical sol-gel and combustion processes claims an extra ordinary importance. Also combustion reaction is self-propagating producing enough temperature which is sufficient for the phase development of ferrimagnetic materials within a very short interval of time (Xi 2006).

In present study, an attempt is made to improve the electrical and magnetic properties of Mn-ferrites with addition of Cu and to synthesize CuxMn1-xFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrites at low temperature via sol-gel auto-combustion method.

2. EXPERIMENTAL PROCEDURES

Analytical grade ferric nitrate Fe(NO3)2.9H2O, manganese nitrate Mn(NO3)2.4H2O, copper nitrate Cu(NO3)2.3H2O, citric acid C6H6O7.2H2O and ammonia were used as starting materials. In to synthesize a series of CuxMn1-xFe2O4 samples, ferric nitrate, copper nitrate and manganese nitrate according to their molar ratio were dissolved in de-ionized water. Liquid ammonia was used to neutralize the mixed solution to a pH value of 7. Afterwards, the neutralized solution was evaporated to dryness by heating at 200 °C on a hot plate along with continuous magnetic stirring. As water evaporated, the solution became viscous and finally appeared in the form of a highly viscous gel, and then further increase in temperature up to about 300 °C led to the ignition of the gel. The dried gel, in a self-propagating combustion reaction, got burnt out completely to form a loose powder.

All the samples were pelletized by exerting the uni-axial pressure of 5 tons for five minutes. The samples were sintered in the muffle furnace at temperature of 300 °C for 4 hours to avoid any crack in the pellets. X-ray diffraction of the samples were carried out using Rigaku D/Max-IIA diffractometer equipped with CuKα (λ=1.5405Å) radiation. Hitachi scanning electron microscope (SEM) was used to examine the microstructure. Since ferrites have very high resistivity so room temperature high resistance meter (HP-model 4329A Japan) was adopted to measure the electrical resistivity of the samples. Magnetic properties were confirmed with a Lake-Shore 7407, vibrating sample magnetometer.

3. RESULTS AND DISCUSSION

The diffraction patterns of the sample series obtained using XRD has been shown in Fig. 1. All the peaks present in the diffraction patterns were matched with ICSD reference No. 00-025-0283, belonging to the Cu(Mn)-ferrite, with cubic-spinel structure. The indexing of the peaks was performed according to the reference pattern (Bayliss

1996). Lattice parameters ‘a’, sintered density ‘ρs’, X-ray density ‘ρx’,(Smit 1959) and porosity P (1- ρ s / ρ x) as a function of ‘Cu’ concentration were determined from the data, as shown in Table 1.

Fig. 1 XRD patterns of all the samples of the series CuxMn1-xFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0)

Table 1 Values of all calculated physical parameters

Value of x

Molar weight

Lattice parameter, (Å)

X-Ray density g/cm3

Bulk density g/cm3

Porosity (%)

Resistivity Ω-cm

Crystallite size

=0.94

cosB

λ

θ

(nm)

0.00 230.628 8.47 5.042 4.780 5.19 5.39×104 68.02

0.11 232.349 8.46 5.097 4.712 7.55 2.91×106 59.50

0.22 234.071 8.44 5.172 4.610 10.86 3.48×106 48.45

0.33 235.792 8.42 5.247 4.430 15.57 4.91×106 40.03

0.44 237.514 8.40 5.323 4.298 19.25 6.16×106 31.56

0.55 239.236 8.39 5.381 4.134 23.17 7.44×106 24.97

Intensity (Arb. Units)

It is noted that lattice parameter decreased from 8.47 Å to 8.39 Å, as shown in Fig. 2 and porosity is increased from 5.19% to 23.17% , as shown in Fig. 3, with the increase in ‘Cu’ concentration from 0.00 to 1.0 in the CuxMn1-xFe2O4 system. This result could be attributed to the fact that the ionic radius of Cu (0.73 Å) is smaller than Mn (0.83 Å) (Predeep 2010). Room temperature DC electrical resistivity was measured by high resistivity meter (HRM). It was observed that the resistivity of the samples increased in the series as the Cu contents were increased from x = 0 and to x = 1, as shown in the Fig. 4. This increase in resistivity might be attributed to the decrease in hopping length.

Fig. 2 Variation of lattice constant with Cu contents

Fig. 3 Variation in porosity with Cu contents

0.0 0.2 0.4 0.6 0.8 1.0

4

6

8

10

12

14

16

18

20

22

24

Porosity (%)

Cu content (x)

0.0 0.2 0.4 0.6 0.8 1.0

8.38

8.40

8.42

8.44

8.46

8.48

Lattice constant 'a' (

Å)

Cu content (x)

Fig. 4 Variation in resistivity with Cu contents

Hopping length is the distance between magnetic ions in the B-site and is dependent on the lattice parameter (Mansour 2005, Shirsath 2010). The electrical conduction mechanism in ferrites has been well explained by the electron hopping model proposed by Heikes and Johnston (Heikes 1957). As it is evident from the literature that both Mn2+ and Cu2+ ions have the preference at octahedral site since both Mn2+ and Cu2+ ferrites belong to the family of inverse spinels (Verwey 1947). As Fe3+ ions have the preference for octahedral B-site, on substitution of Cu for Mn in CuxMn1-xFe2O4 system, both Mn2+ and Cu2+ ions force an equal amount of Fe3+ ions towards tetrahedral A-site whose amount varies with Cu contents in Mn-Cu ferrite. So the involvement of hopping conduction mechanism at large, results in the form of increase in resistivity (Kambale 2009).

The comparative M-H plots of all the samples are shown in Fig. 5. Magnetic moment was calculated by the relation (Joshi 1988):

nB = Mol. Wt. x Ms/5585 ds (1)

where nB is the magnetic moment of all the samples in Boher magnetons. Ms is the saturation magnetization in emu/cc measured with the following formula;

(1 )s s s

M P dσ= − (2)

Here ds is the sintered density, s

σ is the saturation magnetization in emu/g and P is the porosity of all the samples.

Fig. 5 Comparison of M-H loops of all the samples

The value of Ms and nB are shown in Table 2. Both the values have the same trend with the increase in Cu concentration.

Table 2 Parameters concerning with M-H loops of the samples

Value of x

Hopping

Length,a

4

2

(Å)

Ms

(emu/cc) σS (emu/g)

Bohr magnetron nB

Y-K angle (degree)

Coercivity Hc (Oe)

0.00 2.998 29.602 6.532 0.256 28.836 350

0.11 2.994 32.305 7.416 0.285 35.532 627 0.22 2.988 38.410 9.345 0.349 58.447 982 0.33 2.981 30.004 8.022 0.286 69.734 929 0.44 2.974 27.393 7.893 0.271 79.227 646 0.55 2.970 25.050 7.885 0.259 87.879 265

The graph plotted across Ms vs Cu concentration and nB vs Cu concentration are shown in Figs. 6-7. It has been observed that with the increase in Cu concentration, the coercivity increased up to x = 0.4, then it is decreased on further addition of Cu contents up to x = 1.0, as evident in Fig. 8. Here, in the present case, increase in magnetization by increasing Cu contents up to x = 0.4 is actually strengthening the A-B interaction correspondingly between two sub lattices. This can be explained on the basis of ionic distribution among A and B-site. It indicates that both Mn and Cu ions occupy B-site and with the substitution of Cu in MnFe2O4 more and more Fe3+ ions start migrating from A

to B site, which result in the increase of magnetization of B-sub lattice and reduction of magnetization of A-site. This reduced the B-B interaction and the A-B interaction started increasing up to 40% contents of Cu because of the anti-parallel arrangement of magnetic moments of site A and B. This can also be understood by applying Weiss molecular field theory (Rana 2003).

Fig. 6 Plot of Cu concentration vs saturation magnetization

Fig .7 Plot of Cu concentration vs magnetic moment

Fig. 8 Plot of Cu concentration vs coercivity

With continuous substitution of Cu, i.e. above 40% maximum anti parallelism between the diminishing number of Fe (A) and Fe (B) ions could not be maintained against the increasing anti-parallel interaction with the B ions lattice. The magnetization then gets decreased, which can be seen by the decreasing value of effective magnetic moment presented in Table 2. The decrease in the magnetic moment is also due to the less magnetic nature of Cu, having magnetic moment 1.3 µB and spin 1/2 as compared to Mn, having magnetic moment equal to 5 µB and spin 5/2 (Goldman 1990). The weakening of A-B interaction beyond x = 0.40 can be explained on the basis of triangular spin arrangement of Y–K type on B-sub lattice.

Yafet and Kittel (Yafet 1952) attribute this decrease in magnetization to the triangular arrangement of spin, which decreases the A-B interaction. This triangular arrangement in spin has been sorted out in terms of Yafet and Kittel angle. These values have been calculated considering the relation and plotted against Cu concentration in Fig. 9.

The Yafet-Kittel (Y-K) angles have been calculated using the formula (Schwabe 1963):

(6 )cos 5(1 )B y kn x xα−

= + − − (3)

Fig. 9 Plot of Cu concentration vs Y-K angle

The variation in crystallite size is shown in Fig. 10 and the variation in percent porosity with the addition of Cu in Mn1−xCuxFe2O4 has been already shown earlier in Fig. 3. It is well known that for mixed ferrites, the coercivity increases linearly with porosity and decreases with the increase in the crystallite size (Hc ∝ 1/r) (Zaag 1996). Our results describe the decrease in the crystallite size and increase in the porosity with the substitution of Cu in Mn-ferrite. Therefore, the results are in good agreement with the results reported earlier for mixed ferrites (Zaag 1993).

Fig. 10 Variation in crystallite size with Cu contents

The micrographs of all the samples are shown in the Fig. 11. The morphology of the samples as revealed by the SEM images, seem to consist of equi-axed grains, with small variation in sizes. No particles, inclusion or second phase could be identified in any of the samples. The micrographs also reveal that the grain boundary areas are well eroded and the voids are larger in size and number. Two types of porosities were found in all the samples. First, the intergranular and intra granular, and the second, the porosity due to entrapped gas such as oxygen evolved from the dissociation of MnO and CuO.

Fig. 11 Comparison of SEM micrographs of all the samples

4. CONCLUSIONS

Cu substituted CuXMn1-XFe2O4 ferrites cause significant changes in the structural, electrical and magnetic properties. The lattice parameters ‘a’ decreased linearly with the increase in Cu concentration, but porosity get increased with increment in Cu concentration. The room temperature DC electrical resistivity showed an increasing trend whereas the crystallite size got decreased throughout with the increment in Cu contents. Saturation magnetization, magnetic moment and the coercivity showed the same trend i-e first increase and then decrease. The increasing trend was due to the strengthening of A-B interaction due anti parallel arrangement of magnetic moments of site A and B but further increment in Cu, as it is less magnetic than Mn. The demagnetizing influence of non-magnetic material became more dominant and got rid

over the A-B interaction. Also an increasing trend of Yafet-Kittle angle with increment in Cu concentration added to the decrease in A-B interaction. The optimum conditions have been obtained for the composition at x = 0.4 i.e.; Cu0.4Mn0.6Fe2O4 ferrites.

REFERENCES

Ahmed, S.R., Ogale, S.B., Papaefthymiou, G.C., Ramesh, R. and Kofinas, P. (2002), “Magnetic properties of CoFe2O4 nanoparticles synthesized through a block copolymer nanoreactor route”, Appl. Phys. Lett., 80(9), 1616. Bayliss, P., Erd, D.C., Mrose M.E. and Sabina A.P. (1996), Mineral Powder Diffraction File Data Book, 1601 Parklane, Swarthmore, USA. Gajbhiye, N.S., Balaji, G. and Ghafari, M., (2002), “Magnetic Properties of Nanostructured MnFe2O4 Synthesized by Precursor Technique”, Phys. Status Solidi A, 189(2), 357–361. Goldman A. (1990), Modern Ferrite Technology, Van Nostra Reinold, New York. Heikes, R.R. and Johnston, W.D. (1957), “Mechanism of conduction in Li substituted transition metal Oxides”, J. Chem. Phys., 26(3), 582. Joshi, G.K., Khot, A.Y. and Sawant, S.R. (1988), “Magnetisation, curie temperature and Y-K angle studies of Cu substituted and non substituted Ni-Zn mixed ferrites”, Solid State Commun., 65(12), 1593–1595. Kambale, R.C., Shaikh, P.A., Kamble, S.S. and Kolekar, Y.D. (2009), “Effect of cobalt substitution on structural, magnetic and electric properties of nickel ferrite”, J. Alloys Compd., 478(1–2), 599–603. Mansour, S.F. (2005), “Frequency and composition dependence on the dielectric properties for Mg–Zn ferrite”, Egypt. J. Solids, 28 (2), 263-265. Martirosyan, K.S., Avakyan, P.B. and Nersesyan, M.D. (2002), “Phase formation during self-propagating high temperature synthesis of ferrite”, 38 (4), 400-403. Patil, K.C., Aruna, S.T. and Mimani, T. (2002), “Combustion synthesis: an update, Curr. Opin. Solid State Mater. Sci., 6(6), 507–512. Predeep, P., Prasad, A.S., Dolia, S.N., Dhawan, M.S., Das, D., Chaudhuri, S.K. and Ghose, V. (2010), “Nanocrystalline spinel MnCuFeO ferrites synthesis and structural elucidation using X-ray diffraction and positron annihilation techniques”, IEEE

Transactions on magnetics, 46(3), 847 – 851. Ramay, S.M., Saleem, M., Atiq, S., Siddiqi, S.A, Naseem, S. and Anwar, M.S, (2011) “Influence of temperature on structural and magnetic properties of Co0⋅5Mn0⋅5Fe2O4 ferrites”, Bull. Mater. Sci., 34 (7), 1415–1419. Rana M.U. and Abbas, T. (2002), “The effect of Zn substitution on microstructure and magneticproperties of Cu1−xZnxFe2O4 ferrite”, J. Magn. Magn. Mater., 246(1-2), 110-114. Rana, M.U., Islam, M.U. and Abbas, T. (2003), “Magnetic interactions in Cu-substituted manganese ferrites”, Solid State Commun., 126(3), 129-133. Schwabe, E.A. and Campell, D.A. (1963), “Influence of Grain Size on Square- Loop Properties of Lithium Ferrites”, J. Appl. Phys, 34(4), 1251-1253. Shirsath, S.E., Toksha, B.G., Kadam, R.H., Patange, S.M., Mane, D.R., Jangam, G.S. and Ghasemi, A. (2010), “Doping effect of Mn2+ on the magnetic behavior in Ni–Zn

ferrite nanoparticles prepared by sol–gel auto-combustion”, J. Phys. Chem. Solids, 71(12), 1669–1675. Smit, J. and Wijn, H.P.J. (1959), Ferrites, John Wiley, New York. Valenzuela, R. (2005), Magnetic Ceramics, Cambridge University press, London. Verwey, E.J.W. and Heilmann, E.L. (1947), “Physical Properties and Cation Arrangement of Oxides with Spinel Structures I. Cation Arrangement in Spinels”, J. Chem. Phys., 15(4), 174. Wang, Z., Liu, X., Lv, M., Chai, P., Liu, Y. and Meng, J. (2008), “Preparation of ferrite MFe2O4 (M = Co, Ni) ribbons with nanoporous structure and their magnetic properties”, J. Phys. Chem. B, 112 (36), 11292–11297. Xi, G., Yang, L. and Lu, M. (2006), “Study on preparation of nanocrystalline ferrites using spent alkaline Zn–Mn batteries”, Mater. Lett., 60(29–30), 3582–3585. Yafet, Y. and Kittel, C., (1952), “Antiferromagnetic Arrangements in Ferrites”, Phys. Rev, 87(2), 290 –294. Zaag, P.J.V.D., Ruigrok, J.J.M., Noordermeer, A., van Delden M.H.W.M, Por, P.T., Rekveldt M.T., Donnet, D.M. and Chapman, J.N. (1993), “The initial permeability of polycrystalline MnZn ferrites: The influence of domain and microstructure”, J. Appl. Phys., 74 (6), 4085. Zaag, P.J.V.D., Valk P.J.V.D. and Rekveldt, M.T. (1996), “A domain size effect in the magnetic hysteresis of NiZn-ferrites”, Appl. Phys. Lett., 69(19), 2927-30.