A considerable metamagnetic shape memory effect without any prestrain in Ni 46 Cu 4 Mn 38 Sn 12 Heusler alloy

We report the effect of Ni/Mn variation on the exchange bias properties in the bulk Mn-rich Ni 50Àx Mn 37þx Sn 13 (0 x 4) Heusler alloys. The excess Mn content was found to increase the exchange bias field while it decreases the exchange bias blocking temperature (T EB ) from 149 to 9 K. A maximum shift in the hysteresis loop of 377 Oe is observed for the Ni 46 Mn 41 Sn 13 alloy. As compared to Mn/Sn variation, Ni/Mn variation strongly influences the exchange bias properties in Ni-Mn-Sn alloys. We observed that if the Mn content is above 37 at. % in Ni-Mn-Sn alloys, the T EB value would show a decreasing trend either by varying the Ni or Sn content.

The effect of hydrostatic pressure on the magnetic and magnetocaloric properties of Ni2−XMn1+XGa (X = 0, 0.15) Heusler alloys around the martensitic transformation temperature (TM) has been investigated. We find that magnetic field increases and decreases the characteristic transitions temperature for X = 0 and 0.15, respectively, and increases the saturation magnetization of martensite phase for both the alloys. However, the hysteresis width decreases for both the alloys as we increase the magnetic field to 5 T. Application of hydrostatic pressure increases (decreases) the TM for X = 0 and 0.15. Pressure stabilizes the martensite phase with the increase of TM for Ni2MnGa, whereas the austenite phase gets stabilized with the decrease of TM in Ni1.85Mn1.15Ga (x = 0.15). Metamagnetic-like transition is suppressed for both the specimens with increasing pressure. The maximum magnetic entropy change (ΔSM max) is found to reduce from 19.2 J kg−1 K−1 (P = 0) to 6.04 J kg−1 K−1 (P = 9.69 kilobars) around TM for Ni2MnGa and it decreases from 8.9 J kg−1 K−1 (P = 0) to 1.27 J kg−1 K−1 (P = 7.4 kilobars) around TM for Ni1.85Mn1.15Ga.

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The resisitivity of Ni2−XMn1+XGa (X = 0 and 0.15) magnetic shape memory alloys has been investigated as a function of temperature (4–300 K) and hydrostatic pressure up to 30 kilobars. The resistivity is suppressed (X = 0) and enhanced (X = 0.15) with increasing pressure. A change in piezoresistivity with respect to pressure and temperature is observed. The negative and positive piezoresistivity increases with pressure for both the alloys. The residual resistivity and electron-electron scattering factor as a function of pressure reveal that for Ni2MnGa the electron-electron scattering is predominant, while the X = 0.15 specimen is dominated by the electron-magnon scattering. The value of electron-electron scattering factor is positive for both the samples, and it is decreasing (negative trend) for Ni2MnGa and increasing (positive trend) for X = 0.15 with pressure. The martensite transition temperature is found to be increased with the application of external pressure for both samples.