Photoinduced Spin Precession and Ultrafast Demagnetization in Co2FeAl Films With Crossover From In-Plane to Perpendicular Magnetic Easy Axis

Laser-induced spin precession and ultrafast demagnetization were investigated in MgO-capped Co₂ FeAl (MO-CFA) films. Both the Gilbert damping parameter α and the demagnetization time τ $_m$ monotonically increased with the increasing perpendicular magnetic anisotropy as CFA thickness $x$ was reduced to 0.6 nm. The increase in α may be explained by a stronger spin-orbit coupling. The τ$_m$ of an $L2_{1}$ Co₂FeAl film is larger than that of thick MO-CFA, but smaller than that of MO-CFA with $x \le 0.9$ nm, indicating that the restored orbital angular momentum may have a stronger and opposite effect on τ$_m$ compared to the reduced spin polarization in thin MO-CFA.