Study Of Spin-orbit Torques In Nano Heterostructures With Perpendicular Magnetic Anisotropy

Manipulation of the magnetization in thin films via electrical manners is one of the most important topics in the field of spintronics.Specifically,spin-orbit torquedriven magnetization switching has become an important method,which has already attracted widespread attention.This thesis focuses on the study of spin-orbit torque(SOT),and studies the applications in devices,exploration of new materials,and further improvements of spin transmission in typical device structures.The contents are as follows:(1)The current-driven magnetization switching in the Pt/Co/Ru/Co/Pt multilayer has been studied.The stacked structure with crossed anisotropy has been optimized in which the bottom Co layer exhibits perpendicular magnetic anisotropy,the top Co layer exhibits in-plane magnetic anisotropy and the spacer Ru mediates antiferromagnetic interlayer exchange coupling between them.We have confirmed in this structure that both Co layers could be independently switched without any applied magnetic field via SOT.Meanwhile the switching chirality of the Co layer with perpendicular anisotropy could be reversed freely by controlling the magnetization of the Co layer with in-plane anisotropy.Using this unique switching performance of the crossed anisotropic structure,a spin logic device could be utilized to program three different logic gates,including AND,NOT and NAND,at zero magnetic field.(2)We have realized the current-driven magnetization switching in a van der Waals ferromagnet Fe3 Ge Te2.Through the combination of mechanical exfoliation and magnetron sputtering technology,Fe3 Ge Te2/Pt bilayer samples were prepared.Through the electrical transport measurement,the properties of Curie temperature and perpendicular magnetic anisotropy in this novel magnetic material have been characterized.The second harmonic measurement has been carried out to verify and characterize the spin-orbit torque exerting on Fe3 Ge Te2.Finally,the current-driven magnetization switching based on the spin-orbit torque has been realized,and the phase diagram of the critical switching current at various temperatures and magnetic fields has been obtained.(3)We study the spin current transport through an antiferromagnetic Ir Mn insertion layer in a W/Ir Mn(t)/Co Fe B structure by measuring the spin Hall magnetoresistance(SMR)and spin-orbit torque(SOT).The temperature dependences of SMR and SOT effective field indicate that the spin current transmission reaches its maximum at the Néel temperature.However,comparing with the sample without Ir Mn,the spin transmission decreases monotonically as function of the Ir Mn thickness.Our results suggest that the spin current transmission through the Ir Mn layer(from W layer to Co Fe B layer)is mainly mediated by spin-polarized electrons rather than magnons,which is likely due to the absence of the effective excitations of magnons in the Ir Mn layer by the spin-polarized current.