Spin-orbit Torque In CoFeB/Ta/CoFeB

Investigating non-volatile magnetic storage with high speed,high density and low power consumption is one of the most important research areas of spintronics.Recently,utilizing spin-orbit torque(SOT)to switch perpendicularly magnetized single layer and realize writing information has drawn extensive attention.However,the stray field of ferromagnetic materials and the critical current density,which is at least 10~6 A/cm~2,for SOT induced magnetization switching impede the implement of high density and low power consumption magnetic storage.Synthetic antiferromagnets(SAF)are easily to be manipulated like ferromagnets and have zero stray field,high thermal stability and fast magnetic dynamics like antiferromagnets.Replacing ferromagnetic materials by SAF is expected to promote the development of high speed,high density and low power consumption magnetic storage.Based on CoFeB/Ta/CoFeB systems with perpendicular magnetic anisotropy(PMA),we study the spin-orbit torque switching SAF and the Ta thickness dependence of the critical current density for SOT switching.We deposited SAF CoFeB/Ta/CoFeB heterostructure with PMA and interlayer antiferromagnetic coupling.The spin current generated by the spin Hall effect of tantalum would diffuse up and down into adjacent CoFeB layers and exert SOT on the magnetic moment of CoFeB.Consequently,the magnetization could be switched between two antiparallel states with a critical current density of 2.44×10~7A/cm~2 and these phenomenon can be well replicated by solving Stoner-Wohlfarth model and Landau-Lifshitz-Gilbert equation.We deposited CoFeB/Ta/CoFeB systems with strong PMA of upper CoFeB layer and relatively weak PMA of lower CoFeB layer.By varying the Ta thickness,we found the critical current density for SOT switching could be reduced to 2.1×10~5A/cm~2 for samples with Ta thickness of 3nm.Through transportation measurements and magnetization characterization,we found that the reason for this low critical current density is that samples with Ta thickness of 3nm have relative low coercivity and anisotropy.SOT switching SAFs might advance the high density magnetic memories.Critical current density of 10~5A/cm~2 for SOT switching would promote magnetic storage with lower consumption.