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Ferrimagnet GdFeCo characterization for spin-orbitronics: large field-like and damping-like torques

Spintronics is showing promising results in the search for new materials and effects to reduce energy consumption in information technology. Among these materials, ferrimagnets are of special interest, since they can produce large spin currents that trigger the magnetization dynamics of adjacent layers or even their own magnetization. Here, we present a study of the generation of spin current by GdFeCo in a GdFeCo/Cu/NiFe trilayer where the FeCo sublattice magnetization is dominant at room temperature. Magnetic properties such as the saturation magnetization are deduced from magnetometry measurements while damping constant is estimated from spin-torque ferromagnetic resonance (ST-FMR). We show that the overall damping-like (DL) and field-like (FL) effective fields as well as the associated spin Hall angles can be reliably obtained by performing the dependence of ST-FMR by an added dc current. The sum of the spin Hall angles for both the spin Hall effect (SHE) and the spin anomalous Hall effect (SAHE) symmetries are: $θ_{DL}^{SAHE} + θ_{DL}^{SHE}=-0.15 \pm 0.05$ and $θ_{FL}^{SAHE} + θ_{FL}^{SHE}=0.026 \pm 0.005$. From the symmetry of ST-FMR signals we find that $θ_{DL}^{SHE}$ is positive and dominated by the negative $θ_{DL}^{SAHE}$. The present study paves the way for tuning the different symmetries in spin conversion in highly efficient ferrimagnetic systems.