Study On The Unidirectional Spin Hall Magnetoresistance In Magnetic Heterostructure

Today’s society is in the information age,the huge amount of information generated by people’s production and life puts forward new requirements for information storage and processing technology,while microelectronic devices and integrated circuits developed based on the charge properties of electrons are approaching their physical limits.The application of the spin properties of electrons provides a new controllable degree of freedom for the traditional microelectronic devices,and the resulting spintronic devices attract people’s attention;on the other hand,the study and manipulation of the spin properties of electrons has also opened up a new field in condensed matter physics—spintronics,which focuses on the processes of spin generation,transport,diffusion,scattering,absorption,etc.In recent years,the unidirectional spin Hall magnetoresistance（USMR）effect found in non-magnetic heavy metal（NM）/ferromagnet（FM）bilayer magnetic heterostructures has become a convenient and effective method for people to study spin transport,diffusion and scattering.Because of its unique unidirectional nature and rich physical mechanism,it has been used to study the transport of spin current and the interaction between spin current and magneton.In the past,people have focused on the USMR effect caused by the in-plane spin transverse polarization（y-polarization）in bilayer magnetic heterostructures,but there are few studies on USMR in tri-layer or more-layer magnetic heterostructures and non-y-polarization in some special structures.In this paper,we prepared Ta/Pt(t _Pt)/Co Fe B series and L1₁ ordered Cu_100-xPt_x/Co₅₀Pt₅₀ series samples by magnetron sputtering to investigate the USMR in tri-layer magnetic heterostructures and the spin orbital torque（SOT）and USMR caused by out-of-plane spin polarization（z-polarization）in L1₁ Cu Pt/Co Pt.The main innovative results are as follows:1.Based on the spin diffusion equation,the expressions of spin Hall magnetoresistance（SMR）and USMR for bilayer and tri-layer magnetic heterostructures are derived,and the spin density distribution in the structures and the thickness dependence of SMR and USMR are simulated.This work provides a universal method to analyze spin transport and to calculate spin density distribution in multilayers.2.The SMR and USMR of Ta/Pt(t _Pt)/Co Fe B series samples are measured by harmonic longitudinal voltage measurement while the magnetization rotates in the plane.Their dependence on the thickness of Pt layer is fitted by theoretical expression,and the spin transport parameters of Pt are extracted,=1.24 nm,=0.10±0.03.This work verifies the correctness of the theoretical formulations of SMR and USMR for magnetic heterostructures and highlights the role of USMR as a spin transport probe.3.The current-induced magnetization switch curve,Damping-like（DL-）SOT and spin scattering dependent（SD-）UMR of L1₁ Cu Pt/Co Pt samples are measured by pulsed current magnetization switch measurement and harmonic voltage measurement.We estimate the ratio of z-polarization to y-polarization in the structures with the help of the USMR effect,and find that this ratio has a maximum value of 0.032 in the sample with 60%Pt atoms.Furthermore,we obtained the maximum z-polarization efficiency of 0.0028 in this structure.This work provides a feasible method for the measurement of weak unconventional spin polarization.