Spin-orbit Torque Switching of Perpendicular Magnetization in Ferromagnetic Trilayers

Dong-Kyu Lee,Kyung-Jin Lee

doi:10.1038/s41598-020-58669-1

Abstract

In ferromagnetic trilayers, a spin-orbit-induced spin current can have a spin polarization of which direction is deviated from that for the spin Hall effect. Recently, magnetization switching in ferromagnetic trilayers has been proposed and confirmed by the experiments. In this work, we theoretically and numerically investigate the switching current required for perpendicular magnetization switching in ferromagnetic trilayers. We confirm that the tilted spin polarization enables field-free deterministic switching at a lower current than conventional spin-orbit torque or spin-transfer torque switching, offering a possibility for high-density and low-power spin-orbit torque devices. Moreover, we provide analytical expressions of the switching current for an arbitrary spin polarization direction, which will be useful to design spin-orbit torque devices and to interpret spin-orbit torque switching experiments.

Highlights

Current-induced magnetization switching is a basic working principle of magnetic random access memories (MRAMs)
We note that both issues for the spin-orbit torque (SOT)-induced perpendicular magnetization switching originate from the fact that the spin polarization (y) of spin current is orthogonal to the equilibrium magnetization direction (z)
Our main purpose is to provide the analytic expression of the switching current, which can be used as a design rule for SOT-MRAMs based on the aforementioned ferromagnetic trilayers

Summary

Analytical Analysis

Magnetization dynamics driven by a spin current with an arbitrary spin polarization direction is described by the Landau-Lifshitz-Gilbert equation including the both damping-like torque (DLT) and field-like torque (FLT) as, dmdt. One can obtain the expressions for the switching current density Jsw,[2] and tilting angles (θsw,[2], φsw,2) by combining Eqs. One finds that Jsw becomes small as η increases (i.e., spin-z component increases)[27], confirming a possibility to resolve the second issue, i.e., high write current for conventional SOT switching To address this possibility in more detail, we show material parameter and current pulse-width (τ) dependences of Jsw. Figure 2 shows dependences of Jsw on (a) damping constant, (b) effective anisotropy constant, (c) saturation magnetization, and (d) current pulse-width. Isw is obtained from Jsw at case, we assume that

Psw the

Discussion

Additional information