Temperature dependent structural and magnetic properties of Cerium substituted Co–Cr ferrite prepared by auto-combustion method Ghulam Mustafa a , M.U. Islam a , Wanli Zhang b , Yasir Jamil c , M. Asif Iqbal a , Mudassar Hussain a , Mukhtar Ahmad d,n Q1 a Department of Physics, Bahauddin Zakariya University, Multan 60800, Pakistan b State Key Laboratory of Electronic Thin Films and Integrated Devices, UESTC, Chengdu 610054, China c Department of Physics, University of Agriculture, Faisalabad 38040, Pakistan d Department of Physics, COMSATS Institute of Information Technology, Islamabad 44000, Pakistan article info Article history: Received 15 August 2014 Received in revised form 9 November 2014 Accepted 17 November 2014 Keywords: Spinel ferrites Auto-combustion method Rare Earth (Cerium) X-ray diffraction M–H loops abstract The effects of heat treatment on a nano-crystalline spinel ferrite with chemical formula CoCr 0.04 Ce x F e1.96 x O 4 (x ¼0.06) were investigated in the present work. The sample was prepared by the auto-combustion method and then heat treated at 700–1200 °C for 8 h. The sample heat treated at these temperatures was investigated using thermo-gravimetric analyses and differential scanning calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and vibrating sample magnetometery. The XRD patterns and IR spectra confirmed that the synthesized materials were of single phase at and above 900 °C. The average particle size was found to be in the range of 30.8– 63.8 nm estimated by the Scherer formula. IR studies confirm two main absorption bands in the fre- quency range of 400–800 cm 1 arising due to the tetrahedral (A-site) and octahedral (B-site) stretching vibrations. The average grain size increased with the increase of temperature while distribution of particles became homogeneous as observed by scanning electron microscope. The saturation magneti- zation was increased gradually from 7.4 to 59.6 emu/g with the increase of temperature. The coercivity lies in the range of 248–811 Oe as a function of temperature. The obtained results suggest that the in- vestigated materials may be potential candidates for high density recording media applications. & 2014 Published by Elsevier B.V. 1. Introduction Nanomaterials have attracted numerous scientists all over the world due to their versatile and many applications. Nanos- tructured spinel ferrites have been widely used in microwave ab- sorption materials, microwave devices (isolators, circulators, phase shifters), magnetic drug delivery and high density storage media, fabrication of radio frequency coils, transformer core, and tele- communication devices [1]. Cobalt based ferrites are important due to their magnetic properties, high electrical resistivity, high saturation magnetization and low eddy current losses [2]. It is interesting that, the desired structural and magnetic properties of the soft ferrites for a particular application can be tailored by varying the type and amount of substituent into the spinel lattice. Many groups have reported the behavior of ferrites by substituting trivalent ions (Cr 3 þ ,Al 3 þ ) in place of iron Fe 3 þ including rare earths ions [3,4] like cerium, due to its variable electronic struc- ture and its application in making a permanent magnets. In this connection, the effects of rare earth substitution on the properties of spinel ferrites have been reported by many researchers [5–9]. Also magnetization in spinel ferrites is due to the interaction be- tween A and B-sites. M–H square loop with remanance ratio 0.5 is the prime requirement in recording and memory cores [10]. Fur- thermore, the cations in the spinel structure play an important role in determining the magnetocrystalline anisotropy in the 4f– 3d inter-metallic compounds. It is known that the magnetic be- havior of the ferromagnetic oxides is largely governed by the Fe–Fe interaction (the spin coupling of the 3d electrons). By introducing rare earth R-ons into the spinel lattice, the R–Fe interactions also appear (3d–4f coupling), which can lead to small changes in the magnetization and Curie temperature of these ferrites. The R–R interactions are very weak since they result from the indirect 4f– 5d–5d–4f mechanism [11,12]. Huang and Guoa et al. [13–15] have studied the properties of one-dimensional (1D) and quasi-one- dimensional (Q1D) ceramic nanostructures such as fibers, wires, rods, belts, tubes, spirals, and rings. These types of materials have attracted a great interest owing to their potential applications in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials http://dx.doi.org/10.1016/j.jmmm.2014.11.057 0304-8853/& 2014 Published by Elsevier B.V. n Corresponding author. Fax: þ92 61 9210068. E-mail addresses: ghulammustafabzu@gmail.com (G. Mustafa), ahmadmr25@yahoo.com (M. Ahmad). Please cite this article as: G. Mustafa, et al., Journal of Magnetism and Magnetic Materials (2014), http://dx.doi.org/10.1016/j. jmmm.2014.11.057i Journal of Magnetism and Magnetic Materials ∎ (∎∎∎∎) ∎∎∎–∎∎∎