Enhancement of Perpendicular Magnetic Anisotropy and Transmission of   Spin-Hall-Effect-Induced Spin Currents by a Hf Spacer Layer in W/Hf/CoFeB/MgO   Layer
  We report that strong perpendicular magnetic anisotropy of the ferromagnetic layer in a W/CoFeB/MgO multilayer structure can be established by inserting a Hf layer as thin as 0.25 nm between the W and CoFeB layers. The Hf spacer also allows transmission of spin currents generated by an in-plane charge current in the W layer to apply strong spin torque on the CoFeB, thereby enabling current-driven magnetic switching. The antidamping-like and field-like components of the spin torque exerted on a 1 nm CoFeB layer are of comparable magnitudes in this geometry. Both components originate from the spin Hall effect in the underlying W layer. 
Chi-Feng Pai, Minh-Hai Nguyen, Carina Belvin, Luis Henrique   Vilela-Le\~ao, D. C. Ralph, R. A. Buhrman
cond-mat.mtrl-sci cond-mat.mes-hall