Magnetic entropy change and magnetic-field-induced strain in polycrystalline Ni47 Mn32 Ga21 alloy

The Ni-47 Mn-32 Ga-21 polycrystalline alloy is prepared by the directional solidification technique. The components and the microstructure of the alloy are investigated using SEM, metallography and EDS methods. The magnetic entropy change in the process of the structural and magnetic phase transition, and magnetic-field-induced strains with pressure are also studied through analyzing the magnetization as a function of temperature, and the isotherm magnetization and magnetic field-induced strain curves. The results show that there is little difference between the component and the designed component. The alloy is comprised mainly of martensitic phase at room temperature. In the heating process, the magnetic entropy change reaches a maximum value and has a larger peak half width near Curie temperature( 365 K ). The maximum value of the magnetic entropy change is - 1.45 J/kg . K in a magnetic field of 747 kA/m and its peak half width is 21 K. The Ni-47 Mn-32 Ga-21 alloy exhibits excellent free recoverability of the magnetic-field-induced strains at room temperature( 298 K ). The magnetic-field-induced strain reaches a saturated value of - 670 x 10(-6) without extra stress in a field of 480 kA/m. When the compressive stressis parallel to the direction of the magnetic field, the magnetic-field-induced strain increases evidently with the increase of the pressure, which reaches - 1300 x 10(-6) under a pressure of 27.3 MPa. Meanwhile the strain does not reach the saturated value.