Observation of enhanced magnetic pinning in Sm3+ substituted nanocrystalline Mn-Zn ferrites prepared by propellant chemistry route

We report the effect of Sm3+ substitution on the structural and magnetic properties of nanocrystalline Mn(0.5)Zn(0.5)SmyFe(2-y)O(4) (y - 0.00, 0.01, 0.03 and 0.05) samples prepared by propellant chemistry route using a mixture of fuels. Rietveld refinement of XRD patterns confirmed the formation of cubic spinel phase with space group Fd (3) over barm. The lattice parameter values decreased with Sm3+ substitution up to y = 0.03, but with a noticeable increase for the sample with y = 0.05. In all the samples, entire amount of Zn2+ and Sm3+ were found to be present at the A and B sites, respectively. A distribution of Mn2+ ions at the tetrahedral (A) and the octahedral (B) sites of the spinel Mn0.5Zn0.5Fe2O4 was observed. The microstructures of the samples were observed using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). For all the samples, the average crystallite size decreased with increase in Sm3+ concentration, as determined using Williamson-Hall method. The FTIR spectra showed prominent absorption bands at similar to 540 and similar to 390 cm(-1) corresponding to the stretching vibrations of the metal ion complexes at the tetrahedral (A) and the octahedral (B) sites, respectively. Magnetic properties such as saturation magnetization (M-s), remanence (M-r) and magneton number (eta(B)) were found to decrease, while the coercivity (H-c) and reduced remanence (M-r/M-s) of the samples were found to increase with increasing Sm3+ content. The increase in H-c with increase in Sm3+ concentration is interpreted as the enhanced pinning of the magnetic moments at the magnetic defects created by Sm3+ ions, which is further confirmed by Mossbauer spectroscopy through a nearly constant magnetic hyperfine field. This results in an increase in the magnetic particle size in spite of decreasing average crystallite size. Our work suggests that, Sm3+ substitution can be used to alter the magnetic hardness of Mn-Zn ferrites and to enable them to be used as potential materials for various technological applications. (C) 2016 Elsevier B.V. All rights reserved.