Low Temperature Characteristics of Rock Magnetism

Abstract

Since the magnetocrystalline anisotropy constants (K₁, K₂) and the magnetostriction coefficients (λ₁₀₀, λ₁₁₁) of titanomagnetites change appreciably with temperature in the low temperature range, the magnetic susceptibility and remanent magnetization of these minerals depending on these parameters also change markedly with temperature. In particular, the magnetite-rich titanomagnetite has the isotropic point, at which K₁=0, at a low temperature. The marked reduction of magnetocrystalline anisotropy energy around the isotropic point results in some remarkable magnetic phenomena. These phenomena are: -
(a) On cooling, IRM almost vanishes or is sharply reduced at the isotropic temperature, and on subsequent heating, once diminished magnetization is recovered to a certain extent above the isotropic temperature;
(b) By heating from a temperature below the isotropic point to the room temperature in a magnetic field (H), the sample acquires remanent magnetization;
(c) As IRM almost vanishes at the isotropic temperature on cooling and its recovery on heating is of a small amount (<1/5) while TRM's recovery rate is 80%-90%, the procedure of cooling down a rock sample to a temperature below the isotropic point can work as an effective method of cleaning IRM and VRM of magnetites and titanomagnetites.