Exchange Interaction as a Cause of Reverse Thermo-Remanent Magnetism

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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.

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NAGATA, T., UYEDA, S. Exchange Interaction as a Cause of Reverse Thermo-Remanent Magnetism. Nature 184, 890–891 (1959) doi:10.1038/184890a0

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