Optical probe of spin-orbit fields in metallic magnetic structures

We report a novel self-consistent optical approach based on magneto-optical Kerr effect to directly and quantitatively probe the spin-orbit fields of magnetic devices with 1um diffraction limited spatial resolution. The optical probe is exemplified by investigating the spin-orbit fields in a magnetic stack of Ta(5 nm)/CoFeB(1.1 nm)/MgO(2.0 nm)/TaOx with enhanced perpendicular anisotropy. Both field-like and damping-like contributions were measured independently and their coefficients are quantified at $3.3\times 10^{-6}$ and $-2.0\times 10^{-6}Oe/A.cm^{-2}$ respectively. A detailed comparison with standard transport technique is presented in which a very good agreement were found. Our results establish the relevance of the optical methods for studying spin-orbit torque related physics. We acknowledge the support from the National Science Foundation (DMR-1411085) and the~FAME~Center, one of the six centers of STARnet, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.