Structure and Giant Inverse Magnetocaloric Effect of Epitaxial Ni-Co-Mn-Al Films

The structural, magnetic, and magnetocaloric properties of epitaxial Ni-Co-Mn-Al thin flms with different compositions have been studied. The fims were deposited on MgO(001) substrates by co-sputtering on heated substrates. All films show a martensitic transition where the transition temperatures are strongly dependent on the composition. The structure of the martensite phase was shown to be 14M. The metamagnetic martensitic transition occurs from a strong ferromagnetic austenite to a weak magnetic martensite. The structural properties of the films were investigated by atomic force microscopy and temperature dependent X-ray diraction. Magnetic and magnetocaloric properties were analyzed using temperature dependent and isothermal magnetization measurements. We found that Ni41Co10:4Mn34:8Al13:8 films show giant inverse magnetocaloric effects with magnetic entropy change of 5.8 J /kg K for deltaH = 1 T.