Critical Behavior of the Thermal Conductivity near a Magnetic Phase Transition

Abstract

The phenomenological Weiss molecular field approximation (MFA) allows one to use the dominant coupling forces between neighbouring spins in order to desribe the production of a spontaneous magnetisation below the so-called Curie temperature. In the case of ferromagnetic metallic systems such as REAl₂ where RE is any rare earth ion, it was shown under this MFA that the thermal conductivity к shows a marked change in behavior at the Curie temperature. This investigation of к in the temperature range around the Curie point is important for the understanding of the magnetism of such compounds and to obtain quantitative values of the basic physical parameters. We have next calculated the behavior of the thermal localized-spin resistivity versus reduced temperature in the critical region using the formulae given in our previous papers on the basis of a MFA but also taking into account the presence of an external magnetic field. In order to take into account strict non equilibrium conditions and domain effects, we have also added the contribution from the Barkhausen effect near the Curie temperature. Furthermore we discuss the possible observations of magneto-thermal avalanches at a critical organized state in order to measure magnetic wall pinning energies.