The effect of field cooling and field orientation on the martensitic phase transformation in a Ni2MnGa single crystal

The temperature and field dependence of the magnetization in a Ni2MnGa single crystal was measured using a magnetometer with an applied field oriented in the [001] and [011] directions, respectively, of the parent cubic phase. It was found that the magnetic field magnitude and direction could be used to determine the magnetization of the sample during a thermal transformation from the austenitic phase to the martensite phase. This is explained in terms of a magnetic field induced growth of the twin variant having a favorable orientation to the external magnetic field. A model to interpret the magnetic response in terms of aligned twin variants in the shape memory material is discussed.