Gilbert damping and anisotropic magnetoresistance in iron-based alloys

• The two-current model of Campbell and Fert and the concept of scattering resonance are used.
• The compositional dependence of the Gilbert parameter G is emphasized.
• The existence of the scattering resonance leads to a peak of the spin-flip part of G.
• The analogy between G and the anisotropic magnetoresistance is used.
• Verifiable predictions are made about the temperature dependence of G.

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↑ρ↑ and ρ↓ρ↓. We emphasize the part of the Gilbert parameter, called Gsf, generated by spin-flip interband processes. Both Gsf and the anisotropic magnetoresistance ΔρΔρ are proportional to the square of the spin–orbit parameter, and also proportional to ρ↑ρ↑. In bcc alloys of iron with V, Cr, Mo, etc. solutes on the left of iron in the periodic table, ρ↑ρ↑ is increased by a scattering resonance (Gomes and Campbell, 1966, 1968). Then ρ↑ρ↑, ΔρΔρ, 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.