Anomalous pressure effect on the magnetic properties of Ni-Mn based shape memory alloys

The magnetic behavior of three Ni-Mn-(Sn,In) based shape memory alloys are investigated under hydrostatic pressure. Among them, Ni51.2Mn32.8In16(NM-In-16) and Ni51Mn35Sn14 (NM-Sn-14) have their martensitic transition close to room temperature and undergo several magnetic transitions at lower temperatures. They order ferromagnetically at T-CA, which is just above room temperature. However, the ferromagnetism is destroyed by the martensitic transition at T-MS (<T-CA). The ferromagnetic order is revoked further at a lower temperature T-CM (<T-MS) in the martensite phase. The third alloy, namely, Ni50Mn34Sn16 (NM-Sn-16), has a relatively stable ferromagnetic state (Curie point T-CA = 347 K), and it survives below the martensitic transition temperature, T-MS. Our magnetic study under hydrostatic pressure indicates that T-MS and T-CM ( only for the first two alloys) increase systematically with pressure. However, the saturation magnetization at base temperature is found to be an increasing function of pressure for NM-Sn-14 only, and a decreasing trend is observed for the other two alloys. Most interestingly, NM-Sn-14 shows a large enhancement in magnetocaloric effect (MCE) with pressure, whereas the other two compositions show a drop in MCE with pressure. A subtle competition between the change in Ni-Mn hybridization strength and the Mn-Mn magnetic interaction with pressure can be responsible for the observed anomalous behavior. Published by AIP Publishing.