Figure 5: Comparison of MO and transport measurements.
Comparison of ηMO=ΔθK/f⊥ from MO (red circles) and 
from second-harmonic anomalous-Hall/transverse-Hall (black boxes) measurements for a metallic Ta/CoFeB/MgO with OOP anisotropy (Hk>0), (b) Ta/CoFeB/MgO with IP anisotropy (Hk<0) and (d) insulating YIG/Pt. In a, f⊥ and r⊥ are readily available from MOKE/AH measurements. For IP Ta/CoFeB/MgO in b,c shows MOKE and AH measurements with OOP field to extract f⊥ and r⊥, respectively. In a,b the current is parallel to the field while in c ηMR is demonstrated for both current being parallel (black boxes) and at 45° to the field (blue triangles) corresponding to α=0° and 45°, respectively. In d ηMO is expanded by × 1,000 for clarity while the direct comparison of η’s is shown in e. Equation (6) is validated for Ta/CoFeB/MgO regardless of the sign of the anisotropy as shown in a,b demonstrating that both optical and transport signals in Ta/CoFeB/MgO originate in SOT. In a sharp contrast the equation (6) is violated for YIG/Pt system as demonstrated in d,e. In YIG/Pt, the contribution of SOT in transport measurements is significantly overwhelmed by other nonlinear effects (for example, spin-Seebeck effect) resulting in ηMR≫ηMO as illustrated in d. This comparison demonstrates the superiority of MO measurements for studying SOTs in insulating systems.
