Influence of evolving microstructure on magnetic-hysteresis characteristics in polycrystalline nickel–zinc ferrite, Ni0.3Zn0.7Fe2O4

Abstract We report some research findings on the parallel evolutions of microstructural properties and magnetic hysteresis-loop properties; we attempt to elucidate their relationships. The Ni 0.3 Zn 0.7 Fe 2 O 4 toroidal samples were prepared via high-energy ball milling and subsequent moulding; the samples with nanometer/submicron sized compacted powder were sintered from 600 °C to 1400 °C using 100 °C increments. An integrated analysis of phase, microstructural and hysteresis data would point to the existence of three distinct shape-differentiated groups of B–H hysteresis loops which belong to samples with weak, moderate and strong magnetism. The observed grain size with respect to the magnetic-hysteresis behaviour varied from 0.19 μm to 0.23 μm, 0.24 μm to 0.43 μm and 1.07 μm to 4.98 μm for weak, moderate and strong ferromagnetic behaviour respectively. The first occurrence of a strikingly erect and well-defined sigmoid-shape was observable only when sufficient single-phase purity and crystallinity and a sufficiently high volume fraction of multi-domain grains (>0.25 μm) were attained.