Size dependence of spin-torque switching in perpendicular magnetic tunnel junctions

TL;DR

This paper investigates how the size of perpendicular magnetic tunnel junctions influences spin-torque switching, revealing a transition from coherent to domain wall-mediated reversal around 20 nm and deriving the critical diameter for this change.

Contribution

The study provides a detailed simulation analysis of size-dependent switching mechanisms and introduces a macrospin model that accurately predicts reversal dynamics across different sizes.

Findings

Disks smaller than 20 nm switch coherently.

Larger disks involve domain wall dynamics.

Critical diameter for transition is derived.

Abstract

We simulate the spin torque-induced reversal of the magnetization in thin disks with perpendicular anisotropy at zero temperature. Disks typically smaller than 20 nm in diameter exhibit coherent reversal. A domain wall is involved in larger disks. We derive the critical diameter of this transition. Using a proper definition of the critical voltage, a macrospin model can account perfectly for the reversal dynamics when the reversal is coherent. The same critical voltage appears to match with the micromagnetics switching voltage regardless of the switching path.