Study of fully epitaxial Fe/Pt bilayers for spin pumping by ferromagnetic resonance spectroscopy

We present a study of fully epitaxial Fe/Pt bilayers by means of ferromagnetic resonance (FMR) techniques. The dependence of the resonance field H-FMR, the Gilbert damping parameter alpha, and the FMR linewidth on the Pt thickness is presented and compared with reference layers. Since spin pumping is extremely sensitive to the interface properties, a corresponding study is of large importance. By studying fully epitaxial systems, the existence of an almost perfectly single-crystalline ordered interface is ensured. The measured effects, such as the dependence of the resonant field H-FMR on Pt thickness, are thus related to the physics of spin pumping and not to interface disorder effects. The damping parameter alpha has been extracted from the slope of the linewidth dependence on the FMR frequency. By measuring the enhancement of alpha with Pt a value for the effective spin mixing conductance of g(eff) (up arrow down arrow) = (4.9 +/- 0.5) x 10(19) m(-2) is obtained. We observe an opposite behavior in the dependence of H-FMR when compared with reports on YIG/Pt. In addition, the critical role of the proper choice of a reference layer for the estimation of this value is discussed.