Study On The Spin Orbit Effect In Co/Cu/Co Structures

Generally,SOT and magnetoresistance effect in Ferromagnetic/Nonmagnetic bilayers is related to spin current with ?y.Due to the limitation of its symmetry,the deterministic magnetization reversal driven by current cannot be realized in the experiment.Recently,It has been reported that the spin polarization of ?x,?z and their associated spin torque can be induced by current in Ferromagnetic/Nonmagnetic/Ferromagnetic systems due to the magnetization of the ferromagnetic layer break the symmetry of the structures.This provides a new way to deterministic field-free magnetization switching.This paper studies the spin orbit effect in Co/Cu/Co structure with two ferromagnetic layers perpendicular to each other from SOT effect,current driven magnetization reversal process,unidirectional magnetoresistance effect and so on.The main contents of the study are as follows:1)In order to clearly understand the SOT effect in the system,we use the second harmonic Hall voltage(HHV)technique to systematically study the SOT in this system by rotating external field in xy plane.The results indicated that there are DL-SOT and FL-SOT related to spin polarization caused by spin Hall effect(SHE)and spin rotation effect(SRE)in the system.And the angle dependence of the second harmonic signal differs by 90°.Its related SOT efficiency,namely:?SR,DL=0.079,?SH,DL=0.106,?SR,FL=0.012,?SH,FL=0.048.In addition,We study magnetization switching process of perpendicular anisotropic ferromagnetic layer driven by current in this system.The experimental results indicate that currentdriven deterministic field-free magnetization switching can be realized in Co/Cu/Co structure.The reversal polarity is related to the magnetization of the in-plane Co layer.We believed that this is related to the out-of-plane spin polarization induced by spin orbit precession effect(SOPE)at the in-plane Co/Cu interface,but not to interlayer coupling interactions and stray fields.2)In order to prove the existence of unidirectional magnetoresistance effect with spin rotation symmetry(SR-UMR)in the system,we used the second harmonic longitudinal voltage(HLV)to study the unidirectional magnetoresistance effect(UMR)in the system.From the experimential results,we can obtain that not only the unidirectional spin Hall magnetoresistance effect(USMR)exists in the system,but also the unidirectional magnetoresistance effect with spin symmetry(SR-UMR),and the SR-UMR is origin from spin scattering mechanism related to spin accumulation.The DL-SOT effect also contributes to the second harmonic longitudinal resistance.And the USMR and ?x-related DL-SOT effect satisfy sin? while the SR-UMR and ?y-related DL-SOT effect satisfy cos?.We believe that the spin-orbit effect is related to three kinds of spin polarization.Most importantly,the discovery of SR-UMR provides another strong evidence for the existence of the spin current with spin rotation symmetry in FM/NM/FM structures,which should be of great significance in spintronic devices.