Martensitic Transformation and Magnetocaloric Effect in High-Pressure Synthesized Ni₅₃Mn_23.5Ga_23.5 Alloys

The polycrystalline Ni₅₃Mn_23.5Ga_23.5 ferromagnetic alloy was synthesized by high-pressure method. The Ni₅₃Mn_23.5Ga_23.5 ribbons were prepared by melt-spinning; then, the ribbons were pressed to the bulk samples under the 6-GPa high-pressure and heated to 1173 K for 30 min. The surface morphology, phase transition, and magnetocaloric effect (MCE) were investigated in the Ni₅₃Mn_23.5Ga_23.5 bulk sample. Structural analysis and magnetic measurements studies of the bulk samples revealed the martensitic transformation at room temperature with a low thermal hysteresis of magnetization, and the nanocrystalline was observed by atomic force microscope measurements. The Ni₅₃Mn_23.5Ga_23.5 bulk sample exhibits the directionality, and the magnetic properties have the large magnetization and low coercivity when the sample direction of the applied pressure was perpendicular to the direction of the applied magnetic field. The maximum entropy changes (∆S_M) of − 4.8 J/kg K have been obtained at 330 K under the field of 30 kOe in the Ni₅₃Mn_23.5Ga_23.5 bulk sample.