Damping and Magnetic Anisotropy of Epitaxial Fe1.7Ge Ultrathin Films Grown on Ge(111) Substrates

6, 10 and 20nm thick hexagonal Fe1.7Ge thin films have been grown on face-centered-cubic Ge(111) substrates by molecular beam epitaxy. X-ray diffraction investigations revealed an excellent epitaxy of the Fe1.7Ge films, with crystallographic [112¯] and [11¯0] axes lying in the sample plane. Ferromagnetic resonance, magneto-optical Kerr effect and transverse bias initial inverse susceptibility and torque (TBIIST) measurements reveal that the in-plane anisotropy results from the superposition of a uniaxial and a sixfold symmetry terms. The sixfold anisotropy field, which is in agreement with the crystal structure of the samples, increases with the film thickness suggesting an enhancement of the sample quality, while the small uniaxial anisotropy field does not show regular thickness dependence. Frequency and angular dependences of the FMR linewidth show two-magnon scattering and inhomogeneities contributions which depend on the film thickness. A Gilbert damping parameter as low as 0.0064 is found.