Magnetic properties of epitaxial Co2Cr1-xFexAl full Heusler alloy thin films with the L21 structure

Ferromagnetic Co₂Cr_1-xFe_xAl thin films were deposited onto GaAs substrates by co-evaporation with molecular beam epitaxy. The film stoichiometry was obtained by in situ Auger electron spectroscopy analysis. Growth temperature was optimized to be 673 K by identifying superlattice peaks in X-ray diffraction patterns. Isotropic hysteresis with saturation magnetization of 100 emu/cm³ was obtained for x=0. On the other hand, for 0.4 ≤ x ≤ 1, strong uniaxial anisotropy is observed with hard axes. Also by utilizing these films, magnetic tunnel junctions (GaAs/Co₂Cr_1-xFe_xAl/Al-O(or MgO)/Co_0.9Fe_0.1/Ru/Co_0.9Fe_0.1/Au) were fabricated. It showed a very small tunnel magnetoresistance ratio of less than 2% at 5 K. Spin polarization of the film was also estimated. The magnetic properties, especially magnetic moments near the interfaces can be improved by elimination of atomic disorder.