Modulation of magnetic damping constant of Fe2Co films by heavy doping of rare-earth Yb

The effect of rare-earth element Yb doping on modulating the magnetic properties, especially the damping constant, is investigated in a series of amorphous (Fe2Co)((1-x)) Yb-x thin films by the time-resolved magneto-optical Kerr effect at room temperature. A linear decrease of the saturation magnetization and in-plane uniaxial anisotropy field with the increase of x was observed and explained by the diluted effect of non-magnetic Yb doping. The magnetic damping constant performs a remarkable increase with Yb concentration. X-ray photoelectron spectroscopy reveals partial oxidation of Yb, which has large orbital moment and the associated large spin-orbital coupling (SOC) strength and may be responsible for the increased damping constant in contrast with the expected weak SOC and associated low damping constant of metallic Yb doping.