Anatomy of Type-X Spin-Orbit Torque Switching

TL;DR

This paper systematically investigates the properties of type-x spin-orbit torque switching in ferromagnetic layers, revealing advantages for ultrafast, low-current switching in SOT-MRAM devices through simulations and experiments.

Contribution

It provides a comprehensive analysis of type-x SOT switching, including effects of external fields, anisotropy, canting angle, and field-like torque, highlighting its potential for next-generation memory.

Findings

Type-x SOT switching shows lower current at sub-10 ns pulses with positive FLT.

Switching dynamics transform from type-x to type-y with increasing EA canting angle.

Positive FLT assists, negative FLT complicates, type-x switching.

Abstract

Using type-x spin-orbit torque (SOT) switching scheme, in which the easy axis (EA) of the ferromagnetic (FM) layer and the charge current flow direction are collinear, is possible to realize a lower-power-consumption, higher-density, and better-performance SOT magnetoresistive random access memory (SOT-MRAM) as compared to the conventional type-y design. Here, we systematically investigate type-x SOT switching properties by both macrospin and micromagnetic simulations. The out-of-plane external field and anisotropy field dependence of the switching current density ($J_{sw}$) is first examined in the ideal type-x configuration. Next, we study the FM layer canting angle ($\phi_{EA}$) dependence of $J_{sw}$ through macrospin simulations and experiments, which show a transformation of switching dynamics from type-x to type-y with increasing $\phi_{EA}$. By further integrating field-like torque (FLT) into the simulated system, we find that a positive FLT can assist type-x SOT switching while a negative one brings about complex dynamics. More crucially, with the existence of a sizable FLT, type-x switching mode results in a lower critical switching current than type-y at current pulse width less than ~ 10 ns, indicating the advantage of employing type-x design for ultrafast switching using materials systems with FLT. Our work provides a thorough examination of type-x SOT scheme with various device/materials parameters, which can be informative for designing next-generation SOT-MRAM.