We investigate spin pumping phenomena in polycrystalline CoFeB/Pt and CoFeB/Ta bilayers and the correlation between the effective spin-mixing conductance $g_{\mathrm{eff}}^{\uparrow \downarrow }$ and the obtained voltages generated by the spin-to-charge current conversion via the inverse spin Hall effect in the Pt and Ta layers. For this purpose, we measure the in-plane angular dependence of the generated voltages on the external static magnetic field and we apply a model to separate the spin pumping signal from the one generated by the spin rectification effect in the magnetic layer. Our results reveal a dominating role of anomalous Hall effect for the spin rectification effect with CoFeB and a lack of correlation between $g_{\mathrm{eff}}^{\uparrow \downarrow }$ and inverse spin Hall voltages pointing to a strong role of the magnetic proximity effect in Pt in understanding the observed increased damping. This is additionally reflected on the presence of a linear dependency of the Gilbert damping parameter on the Pt thickness.

We present a study of fully epitaxial Fe/Pt bilayers by means of ferromagnetic resonance (FMR) techniques. The dependence of the resonance field $H_{\mathrm{FMR}}$, 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 $H_{\mathrm{FMR}}$ 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 $g_{\mathrm{eff}}^{\uparrow \downarrow }=(4.9\pm 0.5)\times {10}^{19}{\mathrm{m}}^{-2}$ is obtained. We observe an opposite behavior in the dependence of $H_{\mathrm{FMR}}$ 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.

We present angle-dependent measurements of the damping properties of epitaxial Fe layers with MgO, Al, and Pt capping layers. Based on the preferential distribution of lattice defects following the crystal symmetry, we make use of a model of the defect density to separate the contribution of two-magnon scattering to the damping from the isotropic contribution originating in the spin pumping effect, viscous Gilbert damping, and the magnetic proximity effect. The separation of the two-magnon contribution, which depends strongly on the defect density, allows for the measurement of a value of the effective spin mixing conductance that is closer to the value exclusively due to spin pumping. The influence of the defect density for bilayer systems due to the different capping layers and to the unavoidable spread in defect density from sample to sample is thus removed. This shows the potential of studying spin pumping phenomena in fully ordered systems in which this separation is possible, contrary to polycrystalline or amorphous metallic thin films.

We investigate a series of films with different thickness of the Heusler alloy Co ₂ FeAl in order to study the effect of annealing on the interface with a MgO layer and on the bulk magnetic properties. Our results reveal that while the perpendicular interface anisotropy constant K S ⊥ is zero for the as-deposited samples, its value increases with annealing up to a value of 1.14 ± 0.07 mJ m ⁻² for the series annealed at 320 °C and of 2.01 ± 0.7 mJ m ⁻² for the 450 °C annealed series owing to a strong modification of the interface during the thermal treatment. This large value ensures a stabilization of a perpendicular magnetization orientation for an extrapolated thickness below 1.7 nm. The data additionally shows that the in-plane biaxial anisotropy constant has a different evolution with thickness in as-deposited and annealed systems. The Gilbert damping parameter α shows minima for all series for a thickness of 40 nm and an absolute minimum value of 2.8 ± 0.1 × 10 − 3 . The thickness dependence is explained in terms of an inhomogeneous magnetization state generated by the interplay between the different anisotropies of the system and by the crystalline disorder.

Boosting thermoelectric performance is achieved by growing chemically ordered Fe ₂ VAl thin films by sputtering.

We investigate the effect of Al doping on the magnetic properties of the CoFeB alloy. Comparative measurements of the saturation magnetization, the Gilbert damping parameter α, and the exchange constant as a function of the annealing temperature for CoFeB and CoFeAlB thin films are presented. Our results reveal a strong reduction of the magnetization for CoFeAlB in comparison to CoFeB. If the prepared CoFeAlB films are amorphous, the damping parameter α is unaffected by the Al doping in comparison to the CoFeB alloy. In contrast, in the case of a crystalline CoFeAlB film, α is found to be reduced. Furthermore, the x-ray characterization and the evolution of the exchange constant with the annealing temperature indicate a similar crystallization process in both alloys. The data prove that CoFeAlB fulfills the requirements to be considered an attractive candidate for spin torque switching purposes and a reduction of the switching current in comparison with CoFeB is expected.