Dependence on cation distribution of particle size, lattice parameter, and magnetic properties in nanosize Mn-Zn ferrite

In Mn1-xZnxFe2O4 (x=0 to 1) nanosize particles prepared through hydrothermal precipitation we observe a decrease in particle size from 13 to 4 nm with increasing Zn concentration from 0 to 1. The lattice constant, a, for all Mn/Zn concentrations is found to be less than that for the corresponding bulk values. At specific compositions within x=0.35 and 0.5, the temperature dependence of the magnetization exhibits a cusp-like behavior below the temperature at which the nanoparticles undergo a ferri- to para-magnetic transition (T-c). The Curie temperatures, T-c, of the nanoparticles are in the range of 175-500 degreesC, which are much higher than their corresponding bulk values. To explain these unusual features, the strong preferential occupancy of cations in chemically inequivalent A and B sites and the metastable cation distribution in nanoparticles are invoked. (C) 2002 American Institute of Physics.