Effects of heat treatment on the magnetic phase transition and magnetocaloric properties of Mn _1+δAs _1-xSb _x

We studied effects of heat treatment on the magnetic transition and the magnetocaloric effects (MCEs) of Mn _1-δAs _1-xSb _x with x = 0.1 and 0.25. It is found that sintering at an appropriate temperature gives a sharp magnetic transition and hence giant MCEs for Mn _1+δAs _1-xSb _x. In the bulk samples slowly cooled from a liquid state, free Sb was precipitated, which gives rise to compositional deviation. Quenching from a liquid state suppresses the precipitation of Sb. Subsequent annealing is effective to improve homogeneity, as a result, the sample undergoes a sharp magnetic transition. The optimum conditions of heat treatments of the present system for a sharp magnetic transition are discussed.