Research On Spin Wave Film With Out-of-plane Anisotropy And Low-loss Device

In recent years,yttrium-iron garnet film materials with extremely low damping coefficients have become a research hotspot with the in-depth study of spin wave electronic devices.Research indicates that based on the nano-thickness heterojunction constructed by garnet film with perpendicular magnetic anisotropy?PMA?and heavy metal film,spin wave storage and logic devices can be designed based on the anomalous spin Hall effect or inverse spin Hall effect.The spin wave mode allows spin electrons to be transported at the interface between the insulating medium and the metal,which greatly reduces the loss.Moreover,the ultra-thin garnet film can more easily realize the transmission and control of spin waves in the heterojunction.Therefore,the requirements for ultra-thin,PMA,and low damping corresponding to the thin-film materials used for spintronics are proposed.The purpose of this paper is to research thin-film materials suitable for spintronics devices,and progress has been made in anomalous spin Hall devices.On the basis of existing research,bismuth-doped thulium iron garnet film and bismuth-doped yttrium iron garnet film with PMA were epitaxially grown on single crystal GGG and SGGG substrates by radio frequency magnetron sputtering,respectively.The structure and magnetic properties of the film were tested and analyzed,and the anomalous Hall effect tests were performed on the Bi-doped garnet/metal film heterostructures.We prepared films with chemical formulas Tm₂Bi₁Fe₅O₁₂ and Y₂Bi₁Fe₅O₁₂ by RF magnetron sputtering.By controlling the annealing conditions of the film,the stress-induced anisotropy was used to overcome the shape anisotropy,and a series of garnet films with PMA were obtained.The external magnetic field required for magnetization saturation of Tm₂Bi₁Fe₅O₁₂ thin films with thickness of 16 nm and annealed at 900?for 4 h was 35 Oe,the remanence ratio 0.71,the coercive force 2.5Oe.The PMA of the films was reduced due to the relaxation of the stress as the thickness of the film increased.The 64 nm-thick film was saturated with magnetization when the applied magnetic field was 300 Oe,but the easy magnetization axis was still out of plane.Tested at 5 GHz,the ferromagnetic resonance line width of 48nm-thick film was 102.28 Oe and the damping constant 1.23×10^-2.We found that the 20nm-thick Y₂Bi₁Fe₅O₁₂ film had the best PMA under the combined effect of stress-induced anisotropy and surface roughness of the film.The external magnetic field required for magnetization saturation of Y₂Bi₁Fe₅O₁₂ thin films with thickness of 20 nm and annealed at 850?for 2 h was 90 Oe,the remanence ratio 0.8,the coercive force 30Oe.Tested at 8 GHz,the ferromagnetic resonance line width was 35.66 Oe,and the damping constant 3.37×10^-3.The PMA of the films was reduced due to the relaxation of the stress as the thickness of the film increased,and the easy magnetization axis became in-plane as the thickness reached 40 nm.Finally,based on the aforementioned Tm₂Bi₁Fe₅O₁₂ and Y₂Bi₁Fe₅O₁₂ thin films and nano-scale heavy metal Pt thin films,heterojunction devices were integrated.By testing the anomalous Hall effect of Hall bar devices with Tm₂Bi₁Fe₅O₁₂/Pt and Y₂Bi₁Fe₅O₁₂/Pt structures,we discovered:hall bars with different thicknesses of Pt layers were prepared on a Tm₂Bi₁Fe₅O₁₂ thin film of 16 nm.When a 3 mA current was applied in the longitudinal direction,the thickness of the Pt layer was 10 nm,8 nm,and 5 nm,and the lateral Hall voltages were 1.9?V,3.2?V and 5.9?V,respectively.Proved that the films we grow can realize anomalous spin Hall devices,and the conclusion that the anomalous Hall signal increases as the thickness of Pt decreases was verified.