Ferri- to ferro-magnetic transition in the martensitic phase of a Heusler alloy

During the past decade the magnetic properties of Heusler alloys have been extensively studied, motivated in part by the observation of large magnetocaloric effects (MCEs) displayed by these alloys near room temperature. We present new data and develop a consistent mechanism to explain the complex hysteretic behavior of a Ni50Mn35In15 Heusler alloy. The magnetization of this alloy is characterized by two critical temperatures. Below the lower critical temperature, the alloy is a ferrimagnetic martensite. Between the two critical temperatures, the alloy is a ferromagnetic martensite. Above the higher critical temperature, it is a paramagnetic austenite. The transitions at both critical temperatures are first order. The ferri-to-ferromagnetic transition and the crystallographic martensite-to-austenite transition explain the various facets observed in the MZFC and MFC vs. T plots and their variations with increasing magnetic field. The model successfully explains the isothermal M vs. H loops near room temperature, whose behavior is strongly dependent on the initial magnetic state.

► Ni50Mn35In15 Heusler alloy exhibits large MCE peaks near room temperature.
► The alloy's magnetic properties have been studied for refrigeration applications.
► New magnetic data leads to a new model to explain the alloy's complex behavior.
► This paper is controversial because our model differs from the previous model.
► We provide new perspectives on the Heusler alloys complex magnetic behavior.