Gilbert damping and anisotropic magnetoresistance in iron-based alloys

Abstract We use the two-current model of Campbell and Fert to understand the compositional dependence of the Gilbert damping parameter in certain iron alloys. In that model, spin-up and spin-down carriers have different resistivities ρ ↑ and ρ ↓ . We emphasize the part of the Gilbert parameter, called Gsf, generated by spin-flip interband processes. Both Gsf and the anisotropic magnetoresistance Δ ρ are proportional to the square of the spin–orbit parameter, and also proportional to ρ ↑ . In bcc alloys of iron with V, Cr, Mo, etc. solutes on the left of iron in the periodic table, ρ ↑ is increased by a scattering resonance (Gomes and Campbell, 1966, 1968). Then ρ ↑ , Δ ρ , and Gsf all exhibit a peak at the same moderate concentration of the solute. We find the best fit between this theory and existing experimental data of Gilbert damping for Fe-V epitaxial films at room temperature (Cheng, 2006; Scheck et al., 2007). At room temperature, the predicted Gsf peak is masked by a background arising from non-flip intraband processes. At elevated temperatures, the peak is expected to become more prominent, and less hidden in the background.