Magnetic and martensitic transformations of NiMnX(X=In,Sn,Sb) ferromagnetic shape memory alloys

Martensitic and magnetic transformations of the Heusler ${\mathrm{Ni}}_{50}{\mathrm{Mn}}_{50-y}{\mathrm{X}}_y$ ($\mathrm{X}=\mathrm{In}$ , $\mathrm{Sn}$ and $\mathrm{Sb}$ ) alloys were investigated by differential scanning calorimetry measurement and the vibrating sample magnetometry technique. In all these alloy systems, the austenite phase with the ferromagnetic state was transformed into the martensite phase, which means that these Heusler alloys have potential as $\mathrm{Ga}$ -free ferromagnetic shape memory alloys (FSMAs). Furthermore, multiple martensitic transformations, such as two- or three-step martensitic transformations, occur in all these alloy systems. It was confirmed by transmission electron microscopy observation that the crystal structure of the martensite phase is an orthorhombic four-layered structure which has not been reported in other FSMAs. Therefore, the present $\mathrm{Ga}$ -free FSMAs have the great possibility of the appearance of a large magnetic-field-induced strain.