Grain size effects on the magnetic properties of Zn x Mn 1 À x Fe 2 O 4 nanoferrites J.Z. Msomi a,n , T.A. Nhlapo a , T. Moyo a , J. Snyman b , A.M. Strydom b a School of Chemistry and Physics, University of KwaZulu-Natal, P/bag X54001, Durban 4000, South Africa b Department of Physics, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa article info Keywords: Mössbauer spectroscopy Magnetization Nano-particle Ferrite abstract Single phase nanoferrites bearing the chemical formula Zn x Mn 1 Àx Fe 2 O 4 (0 rx r1.0) have been produced under low reaction temperature of 200 1C. The compounds were characterized by X-ray diffraction, Mössbauer and SQUID measurements. The particle size varies between 5 nm and 14 nm. The particle size dependence of the magnetic properties is investigated. Our results indicate spin-glass behavior at temperatures between 100 K and 200 K. The variation of Zn concentration has also significant effects on the structural and magnetic properties. The complex variation of lattice parameter with x is explained on the basis of redistribution of Zn atoms in both tetrahedral (A) and octahedral (B) sites. The 57 Fe Mössbauer effect spectra show paramagnetic spin state in all the compounds. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Magnetic nanoparticles have broad practical applications in important technologies such as ferrofluids, magnetic drug delivery and high density information storage [1]. The unusual properties of nanosized compared to bulk samples have attracted a lot of attention [1–8]. The important features of magnetic nanoparticles are superparamagnetism and surface spins which can lead to canted-spin structures. In the superparamagnetic state there are weak inter-particle magnetic interactions. Super-spin-glass beha- vior can be observed when there is sufficiently strong magnetic interaction and the ensemble of nanoparticles shows a collective behavior [9]. Zn–Mn ferrites are suitable candidates for applica- tions in magnetic fluids, heat transfer systems, magnetoelectric composites, etc. [2]. In this work we have produced Zn x Mn 1 Àx Fe 2 O 4 (0 rx r1.0) nanoferrites under low reaction temperature of 200 1C and investigated the effects of annealing conditions on the magnetic properties. 2. Experimental details Zn x Mn 1 Àx Fe 2 O 4 (0 rx r1.0) nanoparticles were produced by using a hydrothermal process. The starting materials were ZnCl 2 (99.999%), MnCl 2 Á 4H 2 O (99.99%) and FeCl 3 Á 6H 2 O (99%). Required proportions of chlorides were mixed thoroughly to produce 1 g samples. A concentration of 5 M solution of NaOH was then slowly added to the chloride mixture solutions under rapid stirring until pH was 10. The precipitate was washed several times by deionized water and finally by 200 ml of ethanol. The clean precipitate was dispersed in 300 ml of ethylene glycol under rapid stirring. The mixture was then placed in a 600 ml stainless steel pressure vessel (Watlow series model PARR 4842 reactor). The pressure vessel was heated to 200 1C and the gage pressure was allowed to gradually rise to 100 psi. These conditions were held for 6 h. The cooled products after boiling were filtered and washed by deionized water and ethanol. The recovered synthesized powders were dried under 250 W infrared light and homogenized using an agate mortar and a pestle. The XRD patterns of the samples were obtained using a mono- chromatic beam of Co-Kα radiation (λ ¼ 1.7903 Å) on a Phillips diffractometer (type: PW1710). The XRD data were used to confirm formation of cubic spinel phase of the compounds and estimate crystal size and lattice constants. The Mössbauer spectra were recorded at room temperature (300 K) using a conventional constant acceleration Mössbauer spectrometer with a 57 Co source sealed in Rh matrix. The magnetization measurements were performed by using a Quantum Design SQUID magnetometer from 2 K to 380 K. 3. Results and discussion Fig. 1 shows the variation of XRD spectra for Zn x Mn 1 Àx Fe 2 O 4 as a function of Zn concentration (x). All the XRD peaks were successfully indexed to pure cubic spinel structure. The broad Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials 0304-8853/$ - see front matter & 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jmmm.2014.01.012 n Corresponding author. Tel.: þ273 126 072 26; fax: þ273 126 071 14. E-mail address: msomij1@ukzn.ac.za (J.Z. Msomi). Please cite this article as: J.Z. Msomi, et al., Journal of Magnetism and Magnetic Materials (2014), http://dx.doi.org/10.1016/j. jmmm.2014.01.012i Journal of Magnetism and Magnetic Materials ∎ (∎∎∎∎) ∎∎∎–∎∎∎