Thermal relaxations and phase change kinetics in LaFeSi bulk magnetocaloric material

Magnetic cooling (MC) is among the most promising solid-state alternative to vapor- compression refrigeration [1]. It relies on the magnetocaloric effect (MCE) which is a thermal change (i.e. temperature, entropy) induced in a magnetic material by application and removal of a magnetic field. LaFeSi-based alloys figure among the most promising refrigerant for MC because of their large MCE and their non-criticality [6]. Unfortunately, the large MCE exhibited by the LaFeSi is often associated with intrinsic hysteresis and kinetics of the transition. Both reduce the cooling power density of MC devices. Therefore the commonest approach to optimize magnetocaloric material (MCM) has been aimed at the reduction of hysteresis [1]. It needs a meticulous study of the process underlying the phase transition bringing additional information on the energy landscape probed by the material. Here we focus on the thermal dependence of magnetic properties by studying the phase fraction relaxation, extrapolated from the measurement of magnetization as function of temperature and applied field. Moreover, we study the growth and nucleation process during transition and relaxation in the "Kolmogorov, Johnson and Mehl, and Avrami" framework [4].