Cation distribution and Mössbauer spectral studies of Mg 0.2 Mn 0.5 Ni 0.3 In x Fe 2x O 4 ferrites (x = 0.0, 0.05 and 0.10) S. Verma a,⇑ , J. Chand a , K.M. Batoo b , M. Singh a a Department of Physics, Himachal Pradesh University, Summer-Hill, Shimla 171 005, India b King Abdullah Institute of Nanotechnology, King Saud University, Riyadh 11451, Saudi Arabia article info Article history: Received 10 December 2012 Received in revised form 11 February 2013 Accepted 14 February 2013 Available online 28 February 2013 Keywords: Mössbauer spectroscopy Saturation magnetization Nanoparticles Superparamagnetism abstract The effect of substitution of diamagnetic indium ions in Mg–Mn–Ni ferrite with the composition Mg 0.2 Mn 0.5 Ni 0.3 In x Fe 2x O 4 (x = 0.0, 0.05 and 0.10) synthesized by citrate precursor technique has been investigated. Crystallographic and magnetic properties have been investigated using X-ray diffraction, TEM, VSM and Mössbauer spectroscopy. The single phase cubic spinel structure of these samples has been confirmed from X-ray diffraction analyses. In 3+ ions initially prefer tetrahedral A-site up to x = 0.05 due to which saturation magnetization and magnetic moment increases, followed by subsequent decrease when indium ions begin to occupy octahedral B-site for higher concentration of x. Magnetization measurements exhibit Neel’s collinear ferrimagnetic structure for samples up to x = 0.05. Mössbauer spectra of these sam- ples studied at 300 K show two characteristic ferrimagnetic Zeeman sextets for x = 0.0, followed by relax- ation phenomenon corresponding to x = 0.05 and 0.10. Mössbauer measurements also show dependence of Zeeman spectral lines on smaller particle size which is indicative of their superparamagnetic nature. The dependence of Mössbauer parameters such as isomer shift, quadrupole splitting, linewidth and hyperfine magnetic field on In 3+ ions concentration have been discussed. The variation of hyperfine magnetic field with increasing In 3+ ions content has been explained by Neel’s molecular field theory. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The structural, physical, chemical, electrical and magnetic prop- erties of the spinel structure are very important to investigate its applications in various fields. The striking feature of the iron-rich spinels ferrite is their ferrimagnetism. Polycrystalline ferrites are magnetic semiconductors, because ferrites are stable, relatively inexpensive, easily manufactured and have widespread applica- tions in electronics and telecommunication industries due to their interesting structural, electrical and magnetic properties [1]. The crystal structure of these materials controls their physical proper- ties. Magnetic dilution due to substitution of diamagnetic atoms in spinel structure gives rise to interesting magnetic properties. The emergence of nanotechnology has made the study of ferrites at nanoscale quite an interesting subject, both from the fundamen- tal and application point of view [2]. The utility of nanoferrites in the field of information storage, colour imaging, ferrofluids, micro- wave devices and communication technology is gradually increas- ing due to the exciting magnetic properties of the nanoparticles. The magnetic property of ferromagnetic ferrite materials de- pends on the magnetic interactions between cation with magnetic moments which are situated in the tetrahedral A-site and the octahedral B-site [3]. Various parameters like method of prepara- tion, sintering temperature, sintering atmosphere, stoichiometry, porosity and amount of substituted ions are responsible for the cation distribution in ferrites. Detailed analyses of magnetic properties of oxides having the spinel structure are not possible without determining their cation distribution [4]. 57 Fe Mössbauer spectroscopy is a powerful tool because this method can elucidate the local structure through hyperfine interactions and to study the changes in the magnetic property of a ferrite material when it is doped by suitable ions [5]. We have reported that up to x = 0.05, In 3+ ions enter the A-site but for higher values of x i.e. x > 0.05, it enter B-site in Mg 0.2 Mn 0.5 Ni 0.3 In x Fe 2x O 4 ferrites. As the indium concentration was in- creased, the experimental magnetic moment deviate from a value calculated by the Neel model at x = 0.05. At x > 0.05, the measured magnetic moment decrease with increasing indium ions concen- tration. With the addition of In 3+ ions, tetrahedral A-site expands without distortion to accommodate the larger In 3+ ions. But expan- sion of tetrahedral A-site causes induced perturbation on the neighboring octahedral B-site with increasing indium concentra- tion. This may cause the site percolation of In 3+ ions to octahedral B-site even when x < 0.10 [6]. Indium is diamagnetic and initially its ions migrate to the tetrahedral A-site [1,7]. Since indium has relatively large ionic radius, it will be of great interest to know its effect on the crystal structure and cation distribution. 0925-8388/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2013.02.101 ⇑ Corresponding author. E-mail address: apusaan@gmail.com (S. Verma). Journal of Alloys and Compounds 565 (2013) 148–153 Contents lists available at SciVerse ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom