Reversed Thermoremanent Magnetization in Synthetic Titanomagnetites as a Consequence of High Temperature Oxidation

Abstract

Synthetic single crystals of titanomagnetite (Fe_2.4T_0.6O₄) were progressively oxidized at 1, 275°C, under controlled CO/CO₂ atmospheres to simulate the “deuteric oxidation” process which occurs in nature. For moderate degrees of oxidation the resultant phase assemblage comprised two titanomagnetite phases intergrown with hemoilmenite lamellae. During the acquisition of weak-field thermoremanent magnetization (TRM) by the oxidized multiphase samples, the direction of magnetization was found in some cases to be opposite to that of the applied magnetic field. This self-reversal is thought to be due to a negative magnetostatic interaction between the two titanomagnetites. The interaction field was estimated as being of the order of a few hundred Amps per metre and is thought to be magnetostatic in origin. The region of self-reversal was confined to a narrow oxidation range although partial self-reversal was observed over a much wider range.