Title :
Structural and magnetic phase transitions in Ni-Mn-Ga ferromagnetic shape-memory crystals
Author :
Chu, S.Y. ; Gallagher, R. ; De Graef, M. ; McHenry, M.E.
Author_Institution :
Dept. of Mater. Sci. & Eng., Carnegie Mellon Univ., Pittsburgh, PA, USA
fDate :
7/1/2001 12:00:00 AM
Abstract :
We detail crystal growth and characterization of Ni-Mn-Ga ferromagnetic shape-memory alloys (FSMA). Structural characterization includes X-ray Laue diffraction and X-ray diffraction (XRD) using θ-2θ 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
Keywords :
X-ray diffraction; annealing; crystal growth; differential scanning calorimetry; ferromagnetic materials; gallium alloys; magnetic anisotropy; magnetic transitions; magnetisation; manganese alloys; martensitic transformations; nickel alloys; shape memory effects; DC magnetization; Ni-Mn-Ga; Ni2MnGa; Ni52.7Mn22.6Ga24.7; X-ray Laue diffraction; X-ray diffraction; annealing; crystal growth; differential scanning calorimetry; ferromagnetic shape memory alloy; magnetic anisotropy; magnetic phase transition; magnetic torque; martensitic phase transition; structural phase transition; temperature dependence; temperature hysteresis; Calorimetry; Iron alloys; Magnetic anisotropy; Magnetic materials; Magnetization; Perpendicular magnetic anisotropy; Shape memory alloys; Temperature; X-ray diffraction; X-ray scattering;
Journal_Title :
Magnetics, IEEE Transactions on
