Some New Magnetic Phenomena of Hematite Single Crystal

Abstract

Three sets of magnetic measurements of pure natural hematite single crystals have been carried out in the temperature range from 488°K down to 4.2°K. The first set is the magnetization isotherms along a certain direction in the basal plane which show nothing new but confirm Néel's magnetic model of a superposition of a weak ferromagnetism on a normal antiferromagnetism. The second set is the isotherms along the ternary axis which display very unusual form. The analysis of the isotherms shows: (1) that the antiferromagnetic susceptibility-temperature curves, χ-T, are in good agreement with those obtained by Néel and Pauthenet, (2) that the spontaneous magnetization-temperature curves, σ0-T, indicate that there is no evidence of isotropic ferromagnetism, and that the weak anisotropic ferromagnetism in the basal plane above transition and along the ternary axis below transition seems to have the same nature and origin, (3) the wide transition over a hundred degrees takes place gradually and continuously. The third set of the magnetic measurements is the remanent magnetization along the ternary axis. The σR-T curve is very similar to the σ0-T curve. A more general magnetic model has been proposed which explains the experimental data very satisfactorily. From the present model Haigh's data of remanent magnetization of hematite powder seems to be explained naturally.