Room-temperature colossal spin Hall effect in topological insulator Bi_(0.9)_(o.1)(012) thin films for ultra-low-power spin-orbit-torque switching

摘要

Spin-orbit-torque (SOT) switching using the spin Hall effect (SHE) in heavy metals and topological insulators (TIs) has great potential for ultra-low power magnetoresistive random-access memory (MRAM). To be competitive with conventional spin-transfer-torque switching, a pure spin current source with large spin Hall angle ( θSH >1)and high electrical conductivity (cr>105 Q-1m1) is required. However, there is no spin Hall material so far that satisfies these two conditions simultaneously; heavy metals (P-Ta, Pt, W) show highσ 〜105-106Ω1m1but small spin Hall angle (θSH〜0.08-0.4) [1-3], while topological insulators (TIs) have large θ SH〜2-18.8 but lowσ 〜103-104 Q-1m1 [4,5]). Here, we report the colossal SHE effect in conductive TI BiogSbo i(012) thin films (5-10 nm). We demonstrate that Bio.9Sb0.1(012) thin films have large σ 〜2.5x105 Ω1-m-1and colossal θSH〜52 at room temperature [6,7]. Figure 1(a) compare the room-temperature θSH, σ, and spin Hall conductivity osh of several heavy metals and TIs. In term of σ sh, BiSb outperforms the nearest competitor (Pt) by a factor of 30, and other TIs by a factor of 100. Figures 1(b) and 1(c) demonstrate SOT switching in a 100μmx50 μm Hall bar of Bi0.9Sb0.1(012) (5 nm)/Mn0.45Ga0.55 (3 nm) bi-layer with an applied in-plane magnetic field of ±3.5 kOe, respectively. The cntical current density of 1.5x106 A/cm2 for SOT switching of MnGa is one to two orders of magnitude smaller than those using Ta, Pt, or IrMn, confirming the colossal SHE in BiSb(012). Thus, BiSb(012) is the best candidate for the spin current source in SOT-MRAM and possibly the first industrial application of topological insulators.