Acquisition of thermoremanent magnetization in weak magnetic fields

Abstract

By means of a phenomenological model of weak-field thermoremanent magnetization (TRM) it is possible to reproduce the complex behaviour of TRM and partial TRM (pTRM) to a good approximation. The model depicts a sample as a collection of statistically independent magnetization elements, each of which possesses a definite blocking and a definite unblocking temperature. Moreover, for weak fields, linear dependence of remanence on applied field is assumed for each magnetization element. These assumptions are sufficient to derive to first order the experimentally found relations between the different types of pTRMs. The kinematic equation, which is assumed to govern the cooling process in multidomain (MD) material, is obtained from the model when mean-field interaction is taken into account. The phenomenological model is supported by two physical approaches. Using magnetic phase theory the coefficients that occur in the kinematic equation as derived from the phenomenological model can be physically interpreted for an isotropic ensemble of uniaxial MD particles. A rigorous micromagnetic analysis of the thermal equilibrium state proves the linearity of equilibrium remanence as a function of a weak applied field. A statistical argument extends this linearity to weak-field TRM, which may be carried by non-equilibrium states.