Low Temperature Characteristics of Remanent Magnetization of Magnetite

Self-reversal and Recovery Phenomena of Remanent Magnetization

Abstract

Behaviours of remanent magnetization of magnetite are studied for low temperature range from room temperature to liquid nitrogen temperature (-190°C). The remanent magnetization produced at room temperature on magnetite decreases sharply when magnetite is cooled from room temperature to liquid nitrogen temperature, and recovers a certain percentage of the intensity of the original remanent magnetization when heated to the room temperature (recovery phenomenon), or decreases further in the heating. In some of single crystal magnetites, however, the remanent magnetization was found to reverse its direction at about -145°C in the cooling in non-magnetic space.
In order to explain the anomalous behaviours of a remanent magnetization at low temperatures, it is assumed that the heterogenity in the stress distribution or in other physical conditions in a grain would result in a heterogeneous distribution of isotropic points (temperatures at which crystal anisotropy energy becomes minimum) within a grain. On the basis of these assumptions, it is shown that the regions with different isotropic points then would interact magnetostatically with each other resulting in the self-reversal or the recovery phenomenon.
Cobalt was found to show the similar recovery and reversal phenomena of a remanent magnetization when it is cooled from 400°C to room temperature in nonmagnetic space. Since cobalt has an isotropic point at about 250°C, the self-reversal and the recovery phenomena may be explained in the same way as in magnetite.