Evolution of the interfacial perpendicular magnetic anisotropy constant of the Co₂FeAl/MgO interface upon annealing

We investigate a series of films with different thickness of the Heusler alloy Co₂FeAl in order to study the effect of annealing on the interface with a MgO layer and on the bulk magnetic properties. Our results reveal that while the perpendicular interface anisotropy constant $K_S^{\perp }$ is zero for the as-deposited samples, its value increases with annealing up to a value of $1.14\pm 0.07$ mJ m⁻² for the series annealed at 320 °C and of $2.01\pm 0.7$ mJ m⁻² for the 450 °C annealed series owing to a strong modification of the interface during the thermal treatment. This large value ensures a stabilization of a perpendicular magnetization orientation for an extrapolated thickness below 1.7 nm. The data additionally shows that the in-plane biaxial anisotropy constant has a different evolution with thickness in as-deposited and annealed systems. The Gilbert damping parameter α shows minima for all series for a thickness of 40 nm and an absolute minimum value of $2.8\pm 0.1\times {10}^{-3}$. The thickness dependence is explained in terms of an inhomogeneous magnetization state generated by the interplay between the different anisotropies of the system and by the crystalline disorder. (paper)