Study On The Spin-orbit Torque In Nano Heterostructures With Type-T Magnetic Anisotropy

Spintronics focuses on exploiting both the spin and charge freedom of electrons.Tremendous of practical spintronics devices have emerged with the advance of spintronics.Among them,magnetic tunnel junction is the cornerstone of spintronics devices since it is a promising candidate as next-generation non-volatile memories.Therefore,one central research subject of spintronics is to enhance the electrical reading and writing performance of magnetic tunnel junctions.This study concerns both sides and carries out a series of researches on current-induced perpendicular magnetization switching and tunnel magnetoresistance in magnetic tunnel junctions.Details are listed below:（1）Generation of spin currents in ferromagnets has been studied.And switching of perpendicular magnetization driven by two spin currents originated from the spin Hall effect and the anomalous Hall effect in the ferromagnet has been realized.A macrospin model concerns both an in-plane magnetization layer and a perpendicular magnetization layer,i.e.,a T-type macrospin model,is established.Suppose two spin currents are generated through the spin Hall effect and anomalous Hall effect when a current is applied to the in-plane layer.Consequently,the absorption of these two spin currents lead to the switching of perpendicular magnetization.The switching polarity is co-determined by the polarization of the spin current and the direction of the effective in-plane magnetic field.Proper geometry design enables the differentiation of the contribution of the spin Hall effect and the anomalous Hall effect through the switching polarity.Thus,the existence of these two mechanisms in the ferromagnet is confirmed.Next,experiments are carried out to obtain a well-designed T-type film structure.The existence of these two spin currents is validated by the current-induced perpendicular magnetization switching measurements.This part of work paves ways for the developing of heavy-metal free,low cost spintronics devices.（2）An effective perpendicular magnetic field is obtained in a T-type magnetic multilayer,which leads to efficient spin-orbit torque induced perpendicular magnetization switching.Firstly,a T-type macrospin model is established.And we found that in-plane magnetization titles toward the perpendicular direction under the spin-orbit torque when the current is applied on both the in-plane layer and the perpendicular layer.With the interlayer coupling between in-plane magnetization and perpendicular magnetization,perpendicular magnetization experiences an additional perpendicular effective field,which facilitates（hampers）switching of perpendicular magnetization and reduces（increases）the critical current density when two layers experience spin currents with same（opposite）polarity.Next,experiments are carried out to obtain a well-designed T-type film structure.And the effective perpendicular magnetic field is confirmed through perpendicular field-driven perpendicular magnetization switching experiments.This part of work contributes to efficient perpendicular magnetization switching in T-type multilayers.（3）Realization of voltage-controllable tunnel magnetoresistance in Fe₄N magnetic tunnel junctions.A high-quality Fe/Mg Al O_x/Fe/Mg Al O_x/Fe₄N double barrier magnetic tunnel junction is grown on a single crystal Mg O（001）substrate via molecular beam epitaxy.And a bias-dependent tunnel magnetoresistance is experimentally obtained.When a positive（negative）bias voltage is applied,the electrons tunneling from the Fe（Fe₄N）electrode to the Fe₄N（Fe）electrode,the resistance of the antiparallel state is lower（higher）than that of the parallel state,which leads to a negative（positive）TMR ratio.Through an ab initio calculation,it is demonstrated that this effect is caused by the change of tunneling channels,which related to the band structure of Fe₄N near the Fermi level.This part of work paves ways for the development of new spin logic devices.