Magnetocaloric Effect in Quintenary and Sextenary Heusler Alloys*

Measurements on alloys based on the shape-memory compound Ni₂MnGa have revealed large entropy changes, ΔS, in magnetic fields, H. Significant magnetocaloric effects are generally observed in materials containing expensive rare-earth elements like Gd or toxic elements like As. Such materials are ill-suited for commercial magnetic refrigeration applications. In contrast, alloys based on Ni₂MnGa contain relatively inexpensive and non-toxic elements; a large magnetocaloric effect in such materials would be of particular interest. In this talk, we present heat capacity and magnetization measurements on polycrystalline samples of several quintenary and sextenary Heusler alloys. We determined ΔS using heat capacity measurements performed in applied magnetic fields. Isothermal magnetization measurements as a function of H were performed on selected samples at temperatures in the vicinity of the magnetic phase transition. Using a combination of magnetization and heat capacity data, we estimated the adiabatic temperature change, ΔT_a, that results from applying a magnetic field of H = 5 T. The largest value we observed was ΔT_a ~ 3.5 K, but further work may reveal larger effects as chemical compositions are optimized.