Effects of transitional hysteresis on the large magnetocaloric and magnetoresistance properties of Ni-Mn-Co-Sn Heusler alloy

Abstract

Ni-Mn-Co-Sn based Heusler alloys have drawn immense attention lately due to their significant magnetocaloric (MC) and magnetoresistance (MR) properties near their first-order magneto-structural martensite transformation (MT). Here, we have studied the influence of thermal and magnetic hysteretic behaviours in the temperature and field dependent magnetization and resistivity in Ni45Mn39Co5Sn11 bulk Heusler alloy across the MT regime. This is critical since hysteresis losses could significantly compromise the MC and MR properties in these compounds in practical applications. Isothermal X-ray diffraction measurements at different temperatures reveal that the MT temperature is near room temperature in Ni45Mn39Co5Sn11 alloy. Thermodynamic analyses of isothermal field dependent magnetization data result in large isothermal magnetic entropy changes (ΔS = 17–18 J kg−1 K−1) under a field change (ΔH = 8 T) at 364 K across the MT regime. The calculated refrigeration capacity values (RC = 173–179 J kg−1) for decreasing and increasing fields are significant and independent of magnetic hysteresis across the MT regime. A large adiabatic temperature change (│ΔT│ = 10.4 K for ΔH = 8 T at 364 K) is being reported in Ni45Mn39Co5Sn11 Heusler alloy, which makes it promising for MC applications. Further, the influence of martensite-austenite phase fractions on the MC and MR properties in Ni45Mn39Co5Sn11 alloy has been studied across the MT regime using isofield and isothermal magnetic and magneto-transport measurements. A strong correlation has been established between the observed MR (−36.8%) and the transformed austenite phase fraction using both experimental data and theoretical model. The large RC, │ΔT│, MR values close to the room temperature and the role played by the thermal and magnetic hystereses on the MC and MR properties make the Ni45Mn39Co5Sn11 Heusler alloy an interesting material for technological applications in magnetic refrigeration and switching devices.