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

In ${\mathrm{Mn}}_{\text{1−x}}{\mathrm{Zn}}_x{\mathrm{Fe}}_2{\mathrm{O}}_4$ $\text{(x=0}$ 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 $\text{x=0.35}$ 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 ${\mathrm{(T}}_c\mathrm{).}$ The Curie temperatures, $T_c,$ of the nanoparticles are in the range of $\text{175–500\hspace{0.05em}°}\mathrm{C},$ 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.