Measurement independent magnetocaloric effect in Mn-rich Mn-Fe-Ni-Sn (Sb/In) Heusler alloys

We report a systematic study on the magneto-structural transition in Mn-rich Fe-doped Mn-Fe-Ni-Sn(Sb/In) Heusler alloys by keeping the total valence electron concentration (e/alpha ratio) fixed. The martensitic transition (MT) temperature is found to shift by following a proportional relationship with the e/a ratio of the magnetic elements alone. The magnetic entropy change (Delta S-M) across MT for a selected sample (Mn49FeNi40Sn9In) has been estimated from three different measurement methods (isofield magnetization (M) vs temperature (T), isothermal M vs field (H) and heat capacity (HC) vs T). We observed that though the peak value of Delta S-M changes with the measurement methods, the broadened shape of the Delta S-M-T curves and the corresponding cooling power (similar to 140 Jkg(-1)) remains invariant. The equivalent adiabatic temperature change (Delta T) similar to -2.6 K has been obtained from indirect measurements of Delta T. Moreover, an exchange bias field similar to 783 Oe at 5 K and a magnetoresistance of -30% are also obtained in one of these materials.