Structural and magnetic properties of epitaxial Co ₂FeAl films grown on MgO substrates for different growth temperatures

We report the correlation between the crystalline structure, electronic structure and magnetic properties of Co ₂FeAl films as a function of growing temperature both experimentally and theoretically. The Co ₂FeAl film grown at room temperature is initially in the partially disordered B2 state, but then it gains a much higher ordered structure with increasing growing temperature due to its transition from short-range to long-range crystallographic order by surface diffusion. Electron energy loss spectroscopy measurements reveals that the increase in the I(L3)/I(L2) ratio of Co can be attributed to the enhanced ferromagnetic exchange interaction between neighboring Co atoms and the fact that the Co contribution is more dominant than the Fe contribution. As the growing temperature increases, many more unoccupied 3d states in Co are observed, hence the Gilbert damping constant increases due to a strong spin-orbit interaction. We also present the results of highly accurate quasiparticle self-consistent GW calculations and confirm that Co ₂FeAl in an ideal L2 ₁ structure is indeed a half-metal with a well-defined band gap in the minority spin channel.