Perpendicular Magnetic Anisotropy in Co2 FeAl Thin Films: Effect of Annealing Temperature

Co₂FeAl (CFA) thin films of various thicknesses (1 nm ≤ d ≤ 10 nm) have been grown on (001) MgO single-crystal substrates and annealed at different temperatures (T_a). Their magnetic properties have been studied by vibrating sample magnetometry, broadband microstrip ferromagnetic resonance (MS-FMR), and Brillouin light scattering (BLS). The effective magnetization, deduced from the fit of MS-FMR and BLS measurements, linearly decreases with the inverse thickness (1/d) for all the annealing temperatures. This allows quantifying perpendicular surface anisotropy constants of 1.46, 1.71, and 1.29 erg/cm² for T_a = 215 °C, 265 °C, and 315 °C, respectively. The perpendicular magnetization is achieved for the CFA films below a critical thickness that increases with increasing T_a. Moreover, the fourfold anisotropy fields, measured in the in-plane magnetized films, increase with T_a and decrease with respect to the CFA inverse thickness.