Magnetic Phase-Transition Dependence on Nano-to-Micron Grain-Size Microstructural Changes of Mechanically Alloyed and Sintered Ni0.6Zn0.4Fe2O4

The microstructure evolution in several polycrystalline Ni 0.6 Zn 0.4 Fe 2 O 4 samples as a result of a sintering scheme was studied in detail, in parallel with the changes in their magnetic properties. The Ni 0.6 Zn 0.4 Fe 2 O 4 toroidal sample was prepared via mechanical alloying and subsequent molding; the sample with nanometer-sized compacted powder was repeatedly sintered from 600 to 1200 °C with an increment of 25 °C. An integrated analysis of phase, microstructural and hysteresis data pointed to existence of three distinct shape-differentiated groups of B–H hysteresis loops which belong to samples with weak, moderate and strong magnetism (Idza in Mater. Res. Bull. 47:1345–1352, 2012 ), respectively. The real permeability, μ ′, and loss factor, μ ″, increased with grain size which increased due to increase in sintering temperature and these two magnetic properties also seem to belong to three value-differentiated groups corresponding to the same temperature ranges found for the B–H groupings. These groupings are tentatively explained using Snoek’s Law.