Magnetoresistance of Ni-Mn-Ga-Fe ferromagnetic shape memory films

Magnetoresistance (MR) of Ni-Mn-Ga-Fe shape memory films was investigated. The films with different Fe composition were prepared by co-sputtering method. The obtained films were heat-treated at 1073 K for 1 h in a flow of Ar gas. MR was measured by four point probe method at constant temperature by changing magnetic field up to ± 15 kOe. With increasing Fe composition, Curie temperature T_c and saturation magnetization M_s increased and martensitic transformation temperatures decreased. Negative and isotropic MR was found. MR at the magnetic field of 15 kOe increased with increasing temperature. MR of the film without Fe composition was - 0.44 % at 77 K and - 2.19 % at 353 K in martensitic phase. MR of the film containing 6.1 mol% Fe was - 0.30 % at 77 K in martensite phase and - 0.89 % at 353 K in austenitic phase. MR decreased with the increasing Fe composition. The MR of the films at R.T. below T_c was larger than that at 77K. This temperature dependency of the MR suggest that negative MR of the constraint-aged Ni-Mn-Ga-Fe films is attributed to the s conduction electron scattering by the localized d spins in the modified s-d scattering model.