Phase transitions and magnetocaloric effects in intermetallic compounds MnFeX (X=P, As, Si, Ge)

Since the discovery of giant magnetocaloric effect in MnFeP1 As-x(x) compounds, much valuable work has been performed to develop and improve Fe2P-type transition-metal-based magnetic refrigerants. In this article, the recent progress of our studies on fundamental aspects of theoretical considerations and experimental techniques, effects of atomic substitution on the magnetism and magnetocalorics of Fe2P-type intermetallic compounds MnFeX (X=P, As, Ge, Si) is reviewed. Substituting Si (or Ge) for As leads to an As-free new magnetic material MnFeP1-xSi(Ge)(x). These new materials show large magnetocaloric effects resembling MnFe(P, As) near room temperature. Some new physical phenomena, such as huge thermal hysteresis and 'virgin' effect, were found in new materials. On the basis of Landau theory, a theoretical model was developed for studying the mechanism of phase transition in these materials. Our studies reveal that MnFe(P, Si) compound is a very promising material for room-temperature magnetic refrigeration and thermo-magnetic power generation.