Application And Mechanism Of Spin-torque Ferromagnetic Resonance

Spintronics is the study to investigate and develop the new principles,new functions and new devices related to information technology by using both the charge and spin of electrons.As the core carrier of information technology,magnetic recording medium is undergoing a key technological revolution.Due to the non-locality of magnetic field,it will give rise to high energy consumption and low stability if we use the external magnetic field to drive the magnetic moment of the magnetic recording medium.However,the low power consumption,fast and reliable magnetization reversal can be achieved by utilizing the spin orbit torque generated by the pure spin current?directional motion of the spin angular momentum?.Therefore,it is one of the core technologies for building new high-density,high-speed and low-energy devices of information storage and calculation in the future to realize the electrical control of the local magnetic moment by using the spin orbit torques,and it is also the frontier problem in the spintronics at the moment.Nowdays,the research of the spin orbit torques is mainly focus on the nano-magnetic heterostructures with structural symmetry broken.Since the spin orbit coupling?SOC?in bulk is basically determined by the band structure,the effective control of spin orbit coupling only can be realized in heterogeneous nanostructures;On the other hand,there are abundant physical effects and the coupling of multiple degrees of freedom at the interface of the heterostructures,which are important sources of the spin orbit torques;Besides,the effect of spin orbit torques can be enhanced only when the thickness of the magnetic layer is in the nanometer scale.Therefore,the key of the practical application of spin orbit torques is to study the characteristics and mechanism of spin orbit torques in different magnetic nano-heterostructures.Thus,distinguishing and understanding the spin orbit torques in different material systems,and realizing the control of the magnetization by spin orbit torques,have become the key topic in spintronics.Focusing on the above key issues,we proposed the spin-torque ferromagnetic resonance theory based on the anomalous hall effect,studied the magnetization dynamics of ultra-thin films and epitaxial single crystals and explored the spin orbit torques in the new material systems.The main innovative contributions are as follows:1.The magnetization dynamic driven by spin orbit torque was constructed.We addedtwo typical spin orbit torques?SOTs??field-like torque and damping-like torque?generated by current to the magnetization dynamic equation,and the effectivesusceptibility tensor of different SOTs was obtained.This provides the basis for spindynamic studies based on current induced SOTs.2.The theory and research method of spin-torque ferromagnetic resonance?ST-FMR?based on anomalous Hall effect?AHE?was proposed.We proposed the AHE-basedST-FMR theory by making full use of the AHE caused by strong scattering of ultra-thin films and the SOTs caused by SOC.Based on the theory,experimental methodshave been developed for studying the dynamics and effective SOC of the ultra-thinheterostructures.This method can satisfy the research of the frontier materialsystems involved in the current spintronics.3.The unusual SOTs generated by the symmetry broken of structure was discovered.There was SOT with out-of-plane polarization in the center inversion-symmetricbroken system,which was consisted of antiferromagnet?AFM?Mn₂Au and FeNi.According to the thickness dependence relationship of the SOT,both bulk andinterface effect contributed to it.We also observed SOT generated by the structuralsymmetry broken in the Heusler Co₂FeAl,and the crystal orientation dependenceof the SOT was obtained.