Spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films

We experimentally demonstrate spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films. The width of the compositional gradient interface (CGI) between films is varied from 1.4 to 2.0 nm via sputtering. Spin-torque ferromagnetic resonance is observed in the ferromagnetic Ni95Cu5 alloy fabricated on a Ti/W bilayer with the CGI. The positive spin torque increases with decreasing CGI width, but a negative spin torque is superimposed owing to the negative spin Hall effect in bulk tungsten. A structural undulation in the CGI eliminates this variation in positive spin torque. The CGI width dependence of the spin torque is associated with the generation of spin and/or orbital angular momentum flow at the CGI. Spin-torque generation using a CGI expands the range of material choice for magnetic nonvolatile memory applications.

Automated summary

We demonstrate spin-torque generation using a compositional gradient at the interface of titanium and tungsten thin films. By varying the width of the compositional gradient interface (CGI) between films, spin-torque ferromagnetic resonance is observed in a ferromagnetic alloy. The width dependence of the spin torque is associated with the generation of spin and/or orbital angular momentum flow at the CGI.