Perpendicular Magnetic Anisotropy in Co<sub>2</sub> FeAl Thin Films: Effect of Annealing Temperature

Abstract

Co2FeAl (CFA) thin films of various thicknesses (1 nm $\le d \le 10$ 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.