Structural properties and magnetic interactions in Sr-doped Mg-Mn nanoparticle ferrites

As-prepared Mg0.2-xSrxMn0.8Fe2O4 nanoferrites, 0 <= x <= 0.2, were synthesized through the chemical co-precipitation route. The true lattice constant, relative atomic ratio of elements, mean site ionic radii, hopping and bond lengths, site edges, oxygen positional parameter u, specific surface area, strain, Debye temperature and threshold frequency were determined and discussed as functions of Sr2+ content x. Mossbauer spectra showed coexistence of magnetic and paramagnetic phases in all the samples which proved that they have superparamagnetic property. The spectra were analyzed and attributed to two magnetic subpattems and two quadrupole doublets due to Fe3+ ions at the A- and B-sites. This study proved that the quadrupole and isomer shifts, hyperfine magnetic fields, H-A and H-B, quadrupole doublet splitting, Delta E-A and Delta E-B, and outermost line width at the A- and B-sites, respectively, were x dependent, where the cation distribution was estimated. HA and HB proved dependence on the bond length at the corresponding site, whereas Delta E-A and Delta E-B showed dependence on the crystallite size Rand u. FMR spectra indicated a ferrimagnetic nature of all the samples, where the Lande factor, line width and resonance field showed nonlinear dependence on x. TEM images showed that the average particle size ranges 22 -35 nm and ferromagnetically ordered nano clusters may be existed in the samples. (C) 2015 Elsevier B.V. All rights reserved.