Resonant Precession of Magnetization and Precession -- Induced DC voltages in FeGaB Thin Films

TL;DR

This study investigates the origin of dc voltages generated during ferromagnetic resonance in FeGaB thin films, highlighting the roles of spin pumping, interface effects, and the inverse spin Hall effect.

Contribution

It provides a detailed analysis of the mechanisms behind spin pumping and dc voltage generation in amorphous FeGaB films, emphasizing the significance of interface disorder and anomalous Hall effects.

Findings

Self-induced ISHE may account for up to 90% of the symmetric voltage.

Thin film size effects influence magnetization and voltage magnitude.

Interface disorder and anomalous Hall resistivity significantly impact spin-to-charge conversion.

Abstract

Measurements of frequency dependent ferromagnetic resonance (FMR) and spin pumping driven dc voltage (V_{dc}) are reported for amorphous films of Fe_{78}Ga_{13}B_{9} (FeGaB) alloy to address the phenomenon of self-induced inverse spin Hall effect (ISHE) in plain films of metallic ferromagnets. The V_{dc} signal, which is antisymmetric on field reversal, comprises of symmetric and asymmetric Lorentzians centered around the resonance field. Dominant role of thin film size effects is seen in setting the magnitude of static magnetization, V_{dc} and dynamics of magnetization precession in thinner films (\leq 8 nm). The film thickness dependence of magnetization parameters indicates the presence of a magnetically disordered region at the film-substrate interface, which may promote preferential flow of spins generated by the precessing magnetization towards the substrate. However, the V_{dc} signal also draws contributions from rectification effects of a \approx 0.4 \% anisotropic magnetoresistance and a large (\approx 54 n\Omega.m) anomalous Hall resistivity (AHR) of these films which ride over the effect of spin-orbit coupling driven spin-to-charge conversion near the film-substrate interface. We have addressed these data in the framework of the existing theories of electrodynamics of a ferromagnetic film subjected to radio-frequency field in a coplanar waveguide geometry. Our estimation of the self-induced ISHE for the sample with 54 n\Omega.m AHR shows that it may contribute significantly (\approx 90\%) to the measured symmetric voltage. This study is expected to be very useful for fully understanding the spin pumping induced dc voltages in metallic ferromagnets with disordered interfaces and large anomalous Hall effect.