The effect of partial substitution of In by X = Si, Ge and Al on the crystal structure, magnetic properties and resistivity of Ni50Mn35In15 Heusler alloys

The effect of partial substitution of In by X = Si, Ge and Al on the structural, electrical and magnetocaloric properties of Ni50Mn35In15 Heusler alloys was studied using x-ray diffraction, resistivity, magnetization and thermal expansion measurements. It was observed that the presence of X atoms (similar to 7% X) at In sites strongly affects the crystal structure and electric and magnetic behaviours of Ni50Mn35In15. Martensitic (Pmmm space group) and austenitic (Fm (3) over barm) crystal structures were observed at room temperature for Ni50Mn35In14Ge, Ni50Mn35In14Al and Ni50Mn35In14Si. All samples were found to show unidirectional anisotropy at low temperatures (T < 150 K). Giant positive and negative magnetic entropy changes, as large as Delta S-M, + 82 JKg(-1) K-1 (at T = 274 K) and -6.6J Kg(-1) K-1 (at T = 307 K) were found for a magnetic field change of 5 T with X = Si. The net refrigeration capacity was also observed to change significantly. The maximum negative magnetoresistance was found to be 50% for Ni50Mn35In14Si at H = 5 T and T = 284 K. Phase transition temperatures attributed to martensitic transformation and to ferromagnetic ordering in martensitic and austenitic phases were determined. The influence of the interatomic distance on the properties of Ni50Mn35In15 was discussed.