Exchange Interaction as a Cause of Reverse Thermo-Remanent Magnetism

Abstract

WE reported, in 1952, the occurrence of self-reversing thermo-remanent magnetism of the ferromagnetic minerals contained in the hypersthene hornblende dacite pumice of Mount Haruna, Japan¹. The physical mechanism producing this particular phenomenon was at first considered to be one postulated by Néel², that is, a magneto-static interaction during field-cooling, between two ferromagnetic phases (A, and B) with different Curie points (T _cA, and T _cB). We ascertained that the ferromagnetic minerals consist of two distinct phases, A being a cubic titanium-poor titanomagnetite (T _cA∼ 500° C.) and B a rhombohedral solid solution between ilmenite and hæmatite 0.55 FeTiO₃.0.45 Fe₂O₃(T _cB∼ 200° C.)³. The abundance ratio of A, and B was found to be A/B about 0.02. Subsequent investigations have revealed that the ilmenite-hæmatite phase is the only constituent responsible for our reverse thermo-remanent magnetism; the titanomagnetite phase, although more abundant, is irrelevant to the phenomenon⁴.