Structural and magnetic phase transitions in Ni-Mn-Ga ferromagnetic shape-memory crystals

We detail crystal growth and characterization of Ni-Nln-Ga ferromagnetic shape-memory alloys (FSMA). Structural characterization includes x-ray Laue diffraction and x-ray diffraction (XRD) using theta -2 theta scans. Differential scanning calorimetry (DSC) and DC magnetization measurements have been used to probe structural and magnetic phase transformations in these materials. For the first time, the temperature dependence of magnetic torque reveals a variation of the magnetic anisotropy in stoichiometric Ni2MnGa crystals. We also report on the effect of post-annealing on the martensitic phase transition (MPT) temperature. A Ni52.7Mn22.6Ga24.7 crystal exhibits an onset of the transformation at 304 K. The temperature hysteresis during a heating-cooling process and the full width of the transition are observed to be 2 and 10 K, respectively, for this crystal.