Microstructure and magnetic transition in Cr-substituted Mg-Zn spinel ferrite powders prepared via hydrothermal method

Mg-Zn ferrite powder specimens with the nominal composition Mg0.5Zn0.5Cr (x) Fe2-x O-4 (x = 0.0-1.0 with steps of 0.2) were synthesized via hydrothermal method. It is found that all the specimens exhibit a typical spinel structure, and the lattice parameter increases slightly with x, which confirms the substitution of Cr3+ for Fe3+. The average crystallite size first increases but then decreases with x, which is not the same as the results in previous reports on spinels. The particles in specimens are the aggregate of small nanoscale crystallites, and roughly aggregate more extensively with the increasing Cr content. With the increase of x, the saturation magnetization decreases rapidly, and it becomes more and more difficult for the specimens to magnetize to saturation. The increase of coercivity from 0.6 (x = 0.0) to 32.3 kA m(-1) (x = 1.0) shows a transition from a typical soft magnetic behavior to a hard magnetic behavior with the increase of Cr content, which was not reported before.