Ferromagnetic resonance studies of Fe thin films with dilute heavy rare-earth impurities

The structure and magnetic properties of Fe 1− x Gd(Tb) x films prepared by sputtering have been investigated using x-ray diffraction, vibrating sample magnetometer, and ferromagnetic resonance. Magnetic measurements show that the saturation magnetization decreases as the increase of Gd(Tb) content, which agrees with that Gd(Tb) atomic moments align antiparallel with Fe moments. Theoretical fittings of the angular dependence of ferromagnetic resonance field yield the second- and forth-order perpendicular anisotropy constants K ⊥1 and K ⊥2 , which show a spin reorientation with increasing Gd(Tb) doping. The intrinsic contribution of ferromagnetic resonance linewidth as a result of Gilbert damping is separated from the extrinsic contribution because of the inhomogeneity of the films. It is found that the additions of Gd additives do not significantly improve the damping constant, whereas the Tb dopants increase the damping constant from 0.04 without Tb to 0.11 with 19% Tb, thus a remarkable enhancement of 175%.