Magnetoelastic effects and magnetic anisotropy in Ni2MnGa polycrystals

Linear thermal expansion and magnetostriction measurements under a magnetic field up to 20 kOe, applied parallel and perpendicular to the measuring direction and in the temperature range of 10-300 K, have been performed on a Ni2MnGa polycrystal. The effects of zero-field cooling and field cooling on both the self-strain (H=0) and the magnetic-field-induced strain (MFIS) have been studied. We have found that the MFIS strongly depends on whether a magnetic field was applied during the cooling process. The applied magnetic field facilitates the growth of specific orientation variants along the field direction as the sample is cooled down through martensitic transformation. However, the application of a field in the martensitic phase induces a negligible motion of twin boundaries. On this basis, the singular point detection technique performed on polycrystalline specimens results in being the easiest and most direct way by which to determine the anisotropy field in this class of materials. The temperature behavior of the anisotropy constant and field has been determined for Ni2MnGa. (C) 2001 American Institute of Physics.