Ta thickness effect on field-free switching and spin-orbit torque efficiency in a ferromagnetically coupled Co/Ta/CoFeB trilayer

Current induced spin-orbit torque(SOT)switching of magnetization is a promising technology for nonvolatile spintronic memory and logic applications.In this work,we systematically investigated the effect of Ta thickness on the magnetic properties,field-free switching and SOT efficiency in a ferromagnetically coupled Co/Ta/Co Fe B trilayer with perpendicular magnetic anisotropy.We found that both the anisotropy field and coercivity increase with increasing Ta thickness from0.15 nm to 0.4 nm.With further increase of Ta thickness to 0.5 nm,two-step switching is observed,indicating that the two magnetic layers are magnetically decoupled.Measurements of pulse-current induced magnetization switching and harmonic Hall voltages show that the critical switching current density increases while the field-free switching ratio and SOT efficiency decrease with increasing Ta thickness.Both the enhanced spin memory loss and reduced interlayer exchange coupling might be responsible for theβ_(DL)decrease as the Ta spacer thickness increases.The studied structure with the incorporation of a Co Fe B layer is able to realize field-free switching in the strong ferromagnetic coupling region,which may contribute to the further development of magnetic tunnel junctions for better memory applications.

Field-free switching through bulk spin−orbit torque in L10-FePt films deposited on vicinal substrates

L1_(0)-FePt distinguishes itself for its ultrahigh perpendicular magnetic anisotropy(PMA),enabling thermally stabile memory cells to scale down to 3 nm.The recently discovered“bulk”spin−orbit torques in L1_(0)-FePt provide an efficient and scalable way to manipulate the L1_(0)-FePt magnetization.However,the existence of an external field during the switching limits its practical application,and therefore field-free switching of L1_(0)-FePt is highly demanded.In this manuscript,by growing the L1_(0)-FePt film on vicinal MgO(001)substrates,we realize the field-free switching of L1_(0)-FePt.This method is different from previously established strategies as it does not need to add other functional layers or create asymmetry in the film structure.The dependence on the vicinal angle,film thickness,and growth temperature demonstrates a wide operation window for the fieldfree switching of L1_(0)-FePt.We confirm the physical origin of the field-free switching is due to the tilted anisotropy of L1_(0)-FePt induced by the vicinal surface.We also quantitatively characterize the spin-orbit torques in the L1_(0)-FePt films.Our results extend beyond the established strategies to realize field-free switching,and potentially could be applied to mass production.