Enhancement of damping-like field and field-free switching in Co/Pt bilayer films through quantitative engineering of anisotropy gradient

Abstract

Spin–orbit torque (SOT) is an emerging candidate for electrically controlled magnetization switching in low-power and nonvolatile spintronic devices. However, SOT switching of perpendicular magnetization requires an auxiliary field or additional lateral symmetry breaking, which is difficult to achieve in practical applications. In particular, the mechanism of field-free switching through vertical symmetry breaking still lacks a quantitative description. In this work, a vertically asymmetric Co/Pt bilayer has been constructed through quantitative engineering of anisotropy gradient, while keeping the total magnetic thickness of the bilayer constant. Interestingly, the enhanced asymmetry with greater anisotropy gradient would induce higher SOT efficiencies and larger field-free switching ratios. Field-free switching can be attributed to the slight lateral asymmetry caused by the perpendicular anisotropy gradient. The SOT effective-field enhancement and field-free switching through quantitative engineering of the anisotropy gradient not only offer a deeper understanding of current-induced magnetization switching in perpendicularly asymmetric systems but also provide a potential avenue for practical applications of SOT devices at the wafer level.

Heat-Assisted Magnetization Switching in Flexible Spin–Orbit Torque Devices

“…Tremendous effort has been devoted to enhancing the charge-spin conversion efficiency in HM/FM bilayers, either by exploiting novel spin source materials with larger spin Hall angles or by modifying the HM/FM interface to enhance the spin transport efficiency. − Recently, different kinds of two-dimensional materials (MoS 2 , WTe 2 , Fe 3 GeTe 2 , and Fe 4 GeTe 2 ) and topological insulators (Bi 0.9 Sb 0.1 and Bi 2 Sb 3 ) have been investigated due to a larger spin Hall angle and potentially lower switching current density. However, the complex processing and preparation are not conducive to the massive production of SOT spintronic devices. ,− Moreover, voltage-controlled magnetic anisotropy (VCMA) has been proposed as an alternative approach to reducing the SOT switching current.…”