Effect of chemical and external hydrostatic pressure on magnetic and magnetocaloric properties of Pt doped Ni_2MnGa shape memory Heusler alloys

摘要

The magnetocaloric effect (MCE) on Ni_(2-x)Pt_xMnGa (x = 0.2, 0.3 and 1.0) shape memory Heusler alloys around martensite phase transition temperature (T_M) is investigated by varying chemical pressure (Pt concentration). The magnetic entropy change (ΔS_M) decreases with increasing chemical pressure for various external applied magnetic fields up to 3 T, and the width of thermal hysteresis increases with the increases of Pt concentration. The effect of hydrostatic pressure on both T_M and ΔS_M for Ni_(1.8)Pt_(0.2)MnGa is also investigated. We observed that the application of hydrostatic pressure increases T_M (3.5 K/GPa) and stabilizes the martensite phase. The maximum magnetic entropy change (ΔS_(max)) of 9.31 J Kg~(-1) K~(-1)is observed for a field change of 9 T at ambient pressure for Ni_(1.8)Pt_(0.2)MnGa. Further, the application of external pressure leads to the decrease of ΔS_(max) to 5.52 J Kg~(-1) K~(-1) at 0.91 GPa.