Structural and magnetic properties of epitaxial L2 ₁-structured Co ₂(Cr,Fe) Al films grown on GaAs(001) substrates

We have successfully grown both L 21 polycrystalline Co2 CrAl and epitaxial L 21 -structured Co2 FeAl 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 Co2 CrAl film contains atomically disordered phases, which decreases the magnetic moment per f.u., while the Co2 FeAl 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 Co2 CrAl MTJ at 5 K and 9% for the Co2 FeAl 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 Co2 (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.