Spin charge interconversion in synthetic ferrimagnetic Co/Gd bilayers

Spin-orbitronics in ferrimagnets have gained a lot of traction in the field of Nanomagnetism for efficient memory and logic applications. In particular, rare-earth (RE)-transition metal (TM) ferrimagnetic alloys facilitate current-driven operations while exhibiting exciting phenomena such as self-torques, fast current-driven domain wall motion, and single pulse all-optical switching (AOS). Moving towards RE-TM synthetic ferrimagnets (SFiM) enables easier tunability via thickness and interface engineering. In recent years, wide-range single-shot AOS, and spin-orbit torques (SOT) have been reported in SFiM such as Co/Gd multilayers. To understand the SOT and the role of interface effects in a bilayer RE-TM SFiM system, we fabricated bilayers of Co/Gd on SiO₂ substrate with different capping layers such as Al, Pt, and Ta along with reversal of the bilayer stacking order. Moreover, in another series, we inserted Pt or Cu in between Co and Gd. We mainly use the harmonic Hall technique to quantify the SOT. Whereas for spin-to-charge conversion (SCC), we perform spin-pumping ferromagnetic resonance and spin Seebeck experiments. We report a systematic study on magnetic anisotropy and SCC efficiency in these SFiM systems. This ultimately helps us engineer multilayer systems with high SCC efficiency and host favourable static and dynamic properties of spin textures such as skyrmions.