Large inverse magnetic entropy changes and magnetoresistance in the vicinity of a field-induced martensitic transformation in Ni50-x Cox Mn32-y Fey Ga18

Significantly large inverse magnetic entropy changes (Δ S M) and magnetoresistance (MR) were observed at the inverse martensitic phase transitions of the Ga-based magnetic shape memory Heusler alloys: Ni50-x Cox Mn32-y Fey Ga18. The crystal structures of alloys were tetragonal at 300 K and the phase transition temperatures and magnetic properties were found to be correlated with the degree of tetragonal distortion. The maximum peak values of the Δ SM and MR at H=5 T were determined as ≈ (+) 31 J Kg-1 K-1 and ≈-21%, respectively, for x=8 and y=2. The relatively small hysteretic loss and large refrigeration capacity observed in this system make these compounds promising materials for applications. © 2010 American Institute of Physics