Perpendicular magnetization switching by large spin–orbit torques from sputtered Bi₂Te₃*

Abstract

Spin–orbit torque (SOT) effect is considered as an efficient way to switch the magnetization and can inspire various high-performance spintronic devices. Recently, topological insulators (TIs) have gained extensive attention, as they are demonstrated to maintain a large effective spin Hall angle ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>θ</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">SH</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">eff</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> ), even at room temperature. However, molecular beam epitaxy (MBE), as a precise deposition method, is required to guarantee favorable surface states of TIs, which hinders the prospect of TIs towards industrial application. In this paper, we demonstrate that Bi 2 Te 3 films grown by magnetron sputtering can provide a notable SOT effect in the heterostructure with perpendicular magnetic anisotropy CoTb ferrimagnetic alloy. By harmonic Hall measurement, a high SOT efficiency (8.7 ± 0.9 Oe/(10 9 A/m 2 )) and a large <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>θ</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">SH</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">eff</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> (3.3±0.3) are obtained at room temperature. Besides, we also observe an ultra-low critical switching current density (9.7×10 9 A/m 2 ). Moreover, the low-power characteristic of the sputtered Bi 2 Te 3 film is investigated by drawing a comparison with different sputtered SOT sources. Our work may provide an alternative to leverage chalcogenides as a realistic and efficient SOT source in future spintronic devices.

Topics & Concepts