Reversible to irreversible transitions in periodically driven skyrmion systems

B L Brown,C Reichhardt,C J O Reichhardt

doi:10.1088/1367-2630/aaf8dd

Abstract

We examine skyrmions driven periodically over random quenched disorder and show that there is a transition from reversible motion to a state in which the skyrmion trajectories are chaotic or irreversible. We find that the characteristic time required for the system to organize into a steady reversible or irreversible state exhibits a power law divergence near a critical ac drive period, with the same exponent as that observed for reversible to irreversible transitions in periodically sheared colloidal systems, suggesting that the transition can be described as an absorbing phase transition in the directed percolation universality class. We compare our results to the behavior of an overdamped system and show that the Magnus term enhances the irreversible behavior by increasing the number of dynamically accessible orbits. We discuss the implications of this work for skyrmion applications involving the long time repeatable dynamics of dense skyrmion arrays.

Highlights

2009, magnetic skyrmions are nanometer-sized spin textures that have many similarities to vortices in type-II superconductors, in that they form a triangular lattice in the absence of quenched disorder [33,34,35] and undergo driven motion when subjected to an applied current [33, 36,37,38,39,40,41,42,43]
For applications in which it is necessary for dense arrays of interacting skyrmions to maintain reversible motion over many cycles, it is important to develop an understanding of the onset of periodic reversible behaviors and to characterize the irreversible behaviors as a function of the net displacements of the skyrmions under an ac drive
We find power law exponents of ν = 1.33 in the reversible state and ν = 1.31 in the irreversible state for the overdamped system, similar to what we observe for the skyrmion system, indicating that omission of the Magnus term does not appear to change the universality class of the transition

Summary

Introduction

2009, magnetic skyrmions are nanometer-sized spin textures that have many similarities to vortices in type-II superconductors, in that they form a triangular lattice in the absence of quenched disorder [33,34,35] and undergo driven motion when subjected to an applied current [33, 36,37,38,39,40,41,42,43]. The divergence of τ at the reversible–irreversible transition is similar to what is observed in the periodic shearing of dilute colloids [11] and jammed solids [25, 27] as a function of increasing d, and the power law exponent is similar, suggesting that dc is a critical point separating an absorbing reversible state from a fluctuating irreversible state in the directed percolation universality class [12].

Results

Conclusion