Transition from the macrospin to chaotic behaviour by a spin-torque driven magnetization precession of a square nanoelement

TL;DR

This paper uses micromagnetic simulations to show that as the size of a magnetic nanoelement increases, its magnetization precession transitions from a simple macrospin behavior to chaotic dynamics, invalidating the macrospin approximation even at small sizes.

Contribution

It demonstrates the size-dependent transition to chaos in spin-torque driven magnetization precession, challenging previous assumptions about the macrospin approximation validity.

Findings

Macrospin approximation fails at ~30 nm size

Transition to chaos occurs with increasing nanoelement size

Chaotic behavior invalidates simplified models for small nanoelements

Abstract

We demonstrate (using full-scale micromagnetic simulations) that the spin injection driven steady-state precession of a thin magnetic nanoelement exhibit a complicate transition from the quasi-macrospin to the chaotic behaviour with the increasing element size. For nanoelement parameters typical for those used experimentally we have found that the macrospin approximation becomes invalid already for very small nanoelement sizes (~ 30 nm), in contrast to the previously reported results (Li and Zhang, Phys. Rev. B, vol. B68, 024404-1 (2003))