Figure 1: SOT detected with the polar MOKE.

(a) Experimental setup for using polar MOKE to detect the SOT. A lock-in amplifier supplies an ac current through the sample along the z direction, which generates SOF and SOT that rotate the magnetization in-plane and out-of-plane from the xz plane, respectively. The reflected laser polarization changes with the magnetization of the sample because of the MOKE. The change in the polarization is converted to a voltage signal through a series of optical components and a balanced detector. The voltage signal is detected by the same lock-in amplifier. (b) An example experimental result from CoFeB/Pt with a 12 mA bias current and 5 mW laser power. The inset is the magnetization hysteresis of the same sample. (c) The linear bias current dependence of the MOKE response. The laser power is kept at 5 mW with a beam radius of 2 μm, which corresponds to a power density of 4 × 10⁸ W m⁻². (d) The linear laser power dependence of the MOKE response. The bias current is kept at 10 mA, which corresponds to a current density of 4 × 10¹⁰ A m⁻². (e) Determination of the magnitude of the SOT using self-calibration. MOKE voltages are measured as the laser position is held fixed and the sample is moved along the x direction. The bias current is 12 mA. The magnitude of the SOT is determined to be β=1.83±0.7 nm by fitting both MOKE voltage curves because of the SOT and out-of-plane Oersted field.