Deterministic Field-Free Switching of Perpendicular Magnetization by Bulk Mirror Symmetry Broken Bi_1- _xSb_x (012) with High Spin Hall Conductivity.

Abstract

Out-of-plane spin-orbit torque generation in mirror-symmetry-broken materials is a promising approach for current-induced field-free magnetization switching. However, the key challenge lies in identifying materials with high in-plane spin Hall conductivity that simultaneously generate large out-of-plane spin-orbit torque for low-power spintronic applications. Previously studied low-symmetry materials, in which mirror-symmetry breaking is confined to the surface and the spin Hall conductivity is low, have not resolved this challenge. Here, we demonstrate deterministic field-free magnetization switching enabled by the bulk-mirror-symmetry-broken topological material Bi_1- _xSb_x (012) with high in-plane spin Hall conductivity. The power consumption is two orders of magnitude lower than that of heavy-metal-based devices. Spin-torque ferromagnetic resonance measurements confirm the bulk origin of the out-of-plane spin-orbit torque in Bi_1- _xSb_x (012), yielding an out-of-plane spin Hall conductivity of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo>∼</mo> <mspace></mspace> <mn>1.12</mn> <mo>×</mo> <mrow></mrow> <msup><mn>10</mn> <mn>5</mn></msup> <mfrac><mi>ℏ</mi> <mrow><mn>2</mn> <mi>e</mi></mrow> </mfrac> <msup><mi>Ω</mi> <mrow><mo>-</mo> <mn>1</mn></mrow> </msup> <mspace></mspace> <msup><mi>m</mi> <mrow><mo>-</mo> <mn>1</mn></mrow> </msup> </mrow> </math> (for x = 0.2), which is 5.6 times larger than that of TaIrTe₄. Our results establish bulk mirror-symmetry engineering as an effective strategy for designing energy-efficient field-free spin-orbit torque devices.