Skyrmion generation from irreversible fission of stripes in chiral multilayer films

TL;DR

This study reveals that in chiral multilayer films, stripe fission into skyrmions under magnetic field is irreversible, with skyrmions remaining stable even after field removal, driven by thermodynamic material parameters.

Contribution

It demonstrates the irreversibility of skyrmion formation from stripe fission in chiral multilayers and links this behavior to thermodynamic parameters.

Findings

Stripe fission into skyrmions occurs with increasing magnetic field.

Skyrmions do not fuse back into stripes upon field reversal.

Skyrmion density at zero field is governed by thermodynamic parameters.

Abstract

Competing interactions produce finite-size textures in myriad condensed matter systems, typically forming elongated stripe or round bubble domains. Transitions between stripe and bubble phases, driven by field or temperature, are expected to be reversible in nature. Here we report on the distinct character of the analogous transition for nanoscale spin textures in chiral Co/Pt-based multilayer films, known to host N\'{e}el skyrmions, using microscopy, magnetometry, and micromagnetic simulations. Upon increasing field, individual stripes fission into multiple skyrmions, and this transition exhibits a macroscopic signature of irreversibility. Crucially, upon field reversal, the skyrmions do not fuse back into stripes, with many skyrmions retaining their morphology down to zero field. Both the macroscopic irreversibility and the microscopic zero-field skyrmion density are governed by the thermodynamic material parameter determining chiral domain stability. These results establish the thermodynamic and microscopic framework underlying ambient skyrmion generation and stability in chiral multilayer films and provide immediate directions for their functionalization in devices.