Basic problem in the first-order phase transition magnetic refrigeration material

Abstract

Due to the cell volume mutations and the phase transition latent heat existing during phase transition of the first-order phase transition magnetic refrigeration material, many basic problems need to further explore in the magnetization process. In this paper, taking LaFe13-xSixalloys as the research object, we discuss in detail some problems, such as a phase-change, entropy change, isothermal entropy change, adiabatic temperature change, thermal and magnetic hysteresis, the temperature range and magnetic field range in which the ferromagnetic and paramagnetic state coexist, and magnetic refrigeration capacity calculation, The analysis shows that the magnetic entropies calculated by Maxwell equation and Clausius-Clapeyron equation are equivalent when neglecting the contributions of ferromagnetic and paramagnetic state to magnetocaloric effect. The area surrounded by the curve in heating of isothermal magnetization process and curve in cooling of isothermal magnetization process (hysteresis size) is actually the net work done by magnetic field during the heating process and cooling process. The values of magnetic and thermal hysteresis are related to the measurement time: the longer the measurement time, the smaller the hysteresis is. When the transformation is of the equilibrium phase, the hysteresis should be equal to zero. In addition, the temperature and magnetic field induced magnetic transition processes are discussed, and different calculation models of the first-order phase transition material for magnetic refrigeration refrigeration capacity are proposed.