Gilbert damping in NiFeGd compounds: Ferromagnetic resonance versus time-resolved spectroscopy

Engineering the magnetic properties (Gilbert damping, saturation magnetization, exchange stiffness, and magnetic anisotropy) of multicomponent magnetic compounds plays a key role in fundamental magnetism and its applications. Here, we perform a systematic study of (Ni81Fe19)(100-x)Gd-x films with x = 0%, 5%, 9%, and 13% using ferromagnetic resonance (FMR), element-specific time-resolved x-ray magnetic resonance, and femtosecond time-resolved magneto-optical pump-probe techniques. The comparative analysis of field and time domain FMR methods, with complimentary information extracted from the dynamics of high-frequency exchange magnons in ferromagnetic thin films, is used to investigate the dependence of Gilbert damping on the Gd concentration.