Field-free spin–orbit torque driven multi-state reversal in wedged Ta/MgO/CoFeB/MgO heterostructures

Abstract

We report a current-induced four-state magnetization reversal under zero magnetic field in a wedged Ta/MgO/CoFeB/MgO heterostructure with a perpendicular magnetic anisotropy. Anomalous Hall effect and magneto-optical Kerr effect microscopy measurements were performed to demonstrate that the field-free multi-level reversal is jointly determined by the spin–orbit torque effective field that originates from the lack of the lateral inversion symmetry in the wedged stacking structure and the current-induced Oersted field. Moreover, the creation of robust intermediate Hall resistance states in the multi-state switching strongly depends on the current-induced Joule heating. Our results provide a route for the field-free multi-level state reversal, which is significant for fabricating the non-volatile and energy-efficient multi-level memories or artificial neuron devices.

Influence of ferromagnetic interlayer exchange coupling on current-induced magnetization switching and Dzyaloshinskii–Moriya interaction in Co/Pt/Co multilayer system

“…In contrast, in trilayer FM/HM/FM systems, the spin current, with different polarizations at both interfaces, can act on both FM layers, potentially achieving four stable resistance states. This feature makes them attractive for potential use in low-power consumption and high-density memory design 43 and bioinspired neuromorphic computations 16 , 44 .…”

Deterministic multi-level spin orbit torque switching using focused He+ ion beam irradiation

“…has been achieved in PMA heterostructures in many ways. These include stabilizing intermediate multidomain states by means of multi-ferromagnetic layer stacks, [9][10][11][12] wedged magnetic layers, 13,14 ferrimagnetic 15,16 , ferromagnetic/antiferromagnetic structures 17 , or with interleaved interfaces with different spin Hall angles. 18 A different approach defines the multiple levels as a sequence of pinning-depinning states in SOT-driven reversal 19,20 , which has been shown in both irradiated and non-irradiated single magnetic films 21 .…”

“…Furthermore, ion irradiation is compatible with other approaches for realizing multistate memories without altering their physical design, such as more sophisticated magnetic stacks, wedge layers or lithographic patterns. [8][9][10][11][12][13][14][15][16] We believe that the strategy we have outlined proposes a versatile strategy to realize high-density and low-power-consumption SOT-based memory devices and is relevant for future types of computing architecture.…”