Initialization-Free Multistate Memristor: Synergy of Spin-Orbit Torque and Magnetic Fields

TL;DR

This paper introduces a universal, initialization-free method for multistate magnetization switching in spin-orbit torque devices by integrating an external magnetic field, enabling efficient analog computing applications.

Contribution

The study presents a novel experimental approach combining external magnetic fields with SOT-driven switching to achieve multistate magnetization without initialization, verified in specific material stacks.

Findings

Achieved 18 stable multistate configurations.

Demonstrated multistate behavior due to intermediate domain states.

Validated the method through macrospin calculations and experiments.

Abstract

Spin-orbit torque (SOT)-based perpendicularly magnetized memory devices with multistate memory have garnered significant interest due to their applicability in low-power in-memory analog computing. However, current methods are hindered by initialization problems such as prolonged writing duration, and limitations on the number of magnetic states. Consequently, a universal method for achieving multistate in PMA-based stacks remains elusive. Here, we propose a general experimental method for achieving multistate without any initialization step in SOT-driven magnetization switching by integrating an external out-of-plane magnetic field. Motivated by macrospin calculations coupled with micromagnetic simulations, which demonstrate the plausibility of magnetization state changes due to out-of-plane field integration, we experimentally verify multistate behavior in Pt/Co/Pt and W/Pt/Co/AlOx stacks. The occurrence of multistate behavior is attributed to intermediate domain states with N\'eel domain walls. We achieve repeatable 18 multistate configurations with a minimal reduction in retentivity through energy barrier measurements, paving the way for efficient analog computing.