Perpendicular Magnetic Anisotropy Dependence of Exchange Spin Resonance Mode for Ferrimagnetic GdCoFe Nanoscale Thin Films: Implications for High-Speed Spintronic Devices

Both the ferromagnetic and exchange resonance modes were investigated in the ferrimagnetic Gd-x(Co80Fe20)(100-x) nanoscale thin films by using an all-optical pump-probe technique. We observed that the ferromagnetic resonance frequency fFMR significantly increases in the vicinity of the angular momentum compensation point C-A as well as the effective g-factor geff and Gilbert damping parameter as, which could be fitted well with the theoretical calculation by the Kittel equation. Unconventionally, the exchange resonance mode only appears in the range of 25 at. % = x = 27 at. % (Gd-rich) near C-A. The exchange resonance frequency f(exch) shows a monotonic increase with increasing perpendicular anisotropy constant K-z. We report the experimental and theoretical investigations that the fexch not only depends on both the net angular moment and pump-laser fluence but is also dominated by the K-z.