Remanent Magnetization of a Synthetic Hematite Single Crystal

Abstract

The remanence of a virgin sample of a synthetic single crystal of hematite has been carefully measured along different directions through a temperature range between 77° and 420°K. The effect of a directive field as applied through the low temperature transition on the remanence also has been studied. Some remarkable phenomena in contrast with those of the natural crystal have been recognized. (1) There is no weak ferromagnetism along the [111] direction. (2) The weak ferromagnetism is strictly limited to the (111) plane above the Morin transition and sharply reduced to zero below 259°K. The thermal hysteresis of the remanence-temperature curve forms a perfect square loop. (3) If the sample were warmed through transition in zero external magnetic field no ferromagnetism could be observed along any direction in the crystal. This leads to the conclusion that the antiferromagnetic axes form equilateral triangular arrangment in the basal plane (111) above transition. The experimental data support the phenomenological theory of weak ferromagnetism of Dzyaloshinsky and Vonsovsky.