THERMAL HYSTERESIS OF THE INITIAL PERMEABILITY IN SOFT FERRITES AT TRANSITION-TEMPERATURES

The initial permeability of soft polycrystalline ferrites exhibits thermal hysteresis when the temperature is cycled from above the Curie temperature T(C) to below. The temperature loops are classified into two categories according to the presence or absence of a secondary peak (SP), in addition to the Hopkinson peak, in the thermal spectra. Hysteresis is studied in detail in this work. The role of the transition points T(C) and T(SP) (SP for secondary peak) is shown. The hysteresis is explained by taking into account domain wall pinning and competition between the intrinsic parameters M(S) and K1 around the transition points. This explanation seems to support the fundamental role of a domain wall mechanism in the magnetization process and the idea of a domain wall topography specific to toroidal soft ferrite samples.