We demonstrate spin orbit torque (SOT) magnetization switching of (Pt/Co) multilayers with large perpendicular magnetic anisotropy (PMA) by a topological insulator Bi0.85Sb0.15 layer in both thermal activation and non-thermal regime with current pulse width τ down to 1 ns. For this purpose, we deposited a stack of Bi0.85Sb0.15(10 nm)/Pt(0.4 nm)/Co(0.4 nm)2/insulating buffer on a Si/SiOx substrate by magnetron sputtering, as shown in Fig. 1(a). The (Pt/Co) multilayers have a large PMA with anisotropy magnetic field of 6 kOe. We then fabricated 1000 nm × 800 nm Hall bar devices for ultrafast SOT switching measurement. Figure 1 (b) shows the threshold switching current density JBiSbth as a function of τ at Hx = 1 kOe. The red dashed line is fitting by the thermal activation model (τ >> 10 ns), which yields a zero-Kelvin JBiSbth0 = 2.5×106 A/cm2. Meanwhile, the green dashed line is fitting for the non-thermal regime (τ < 10 ns), which yields a larger JBiSbth0 = 4.1×106 A/cm2 but still smaller than those observed in heavy metals by nearly two orders of magnitude. Figure 1(c) shows SOT switching loops at various t from 4 ns to 1 ns. From time-resolved measurement using 1 ns pulses, we observed a fast domain wall velocity of 470 m/s at a modest JBiSb =1.6×107 A/cm2. We then successfully demonstrated deterministic SOT switching in our device by multi pulses (JBiSb =1.3×107 A/cm2, τ = 3 ns) at Hx = -1 kOe and +1 kOe as shown in Fig. 2. These results demonstrate the potential of BiSb topological insulator for ultralow power and ultrafast operation of SOT-based spintronic devices 1,2.

References 1 N. H. D. Khang, et al, Nature Mater. 17, 808 (2018). 2 N. H. D. Khang, et al, Appl. Phys. Lett. 120, 152401 (2022).