Femtosecond laser excitation of spin resonances in amorphous ferrimagnetic Gd(1-x)Co(x) alloys.

Using 100 fs laser pulses, a high-frequency exchange and a low-frequency ferromagnetic resonance mode have been excited and detected in an amorphous Gd(1-x)Co(x) (78≤x≤85) ferrimagnetic thin film, on both sides of its angular momentum compensation composition. The excitation efficiency of these modes strongly depends on the amount of laser-induced heating. Ways of selectively and efficiently exciting either one or both of these two coexisting magnetic modes by adjusting laser pulse intensity are demonstrated.