Structural and magnetic properties of epitaxial L2_1-structured Co_2(Cr,Fe)Al films grown on GaAs(001) substrates

摘要

We have successfully grown both L2_1 polycrystalline Co_2CrAl and epitaxial L2_1 -structured Co_2FeAl films onto GaAs(001) substrates under an optimized condition. Both structural and magnetic analyses reveal the detailed growth mechanism of the alloys, and suggest that the Co_2CrAl film contains atomically disordered phases, which decreases the magnetic moment per f.u., while the Co_2FeAl film satisfies the generalized Slater-Pauling behavior. By using these films, magnetic tunnel junctions (MTJs) have been fabricated, showing 2% tunnel magnetoresistance (TMR) for the Co_2CrAl MTJ at 5 K and 9% for the Co_2FeAl MTJ at room temperature (RT). Even though the TMR ratio still needs to be improved for future device applications, these results explicitly include that the Co_2(Cr,Fe)Al full Heusler alloy is a promising compound to achieve half-metallicity at RT by controlling both disorder and surface structures in the atomic level by manipulating the Fe concentration.