Fig. 2. Writing current effect on the spin signal.

(A and B) Schematic four-terminal device structures and measurement setups for writing current and spin potentiometry. (C to H) Voltage detected by the FM contact as a function of in-plane magnetic field measured on device B at the relatively small I_d of 0.5 μA (C, E, and G) and −0.5 μA (D, F, and H) after applying a large I_w of −40 μA for 2 hours (C and D), 50 μA for 0.5 hours (E and F), and −40 μA for 3 hours (G and H). The trend of the B field–induced voltage change, which measures the direction of the channel spin polarization, is independent of the relatively small I_d but is set by the direction of the large I_w (applied at B = 0 T and before the spin potentiometric measurement). The directions of I_d, I_w, channel spin polarization S as determined by the spin signal, and Py magnetization M are labeled by the corresponding arrows. All the measurements are performed at T = 1.6 K.