The influence of composition change on structural and magnetic properties of non-stoichiometric Ni-Mn-Ga alloys

The influence of Ni substituted for Mn and that of Mn for Ga on structural and magnetic properties of non-stoichiometric arc-melted Ni-Mn-Ga alloys is studied. X-ray powder diffraction analysis shows typical Heusler structures for all the samples prepared. The magnetization of the alloys as a function of temperature shows sharp transitions from martensitic tetragonal to austenitic cubic states and from ferromagnetic to paramagnetic upon heating. It is also found that T_M strongly increases and T_C decreases with increasing Ni and Mn concentrations. Magnetic field-induced strain, magnetocaloric effect and anisotropy are also investigated by measuring the thermal expansion upon heating of the sample after ZFC and FC and by using singular point detection technique, respectively. The results indicate that the applied magnetic field facilitates the growth of specific orientation variants along the field direction as the sample is cooled down through the martensitic transition.