Comparison of skyrmion phases between poly and single-crystal MnSi by composite magnetoelectric method

TL;DR

This study compares skyrmion phases in polycrystalline and single-crystal MnSi using a composite magnetoelectric method, revealing differences in phase behavior, depinning thresholds, and the influence of grain boundaries on skyrmion dynamics.

Contribution

It introduces a novel application of the composite magnetoelectric method to analyze skyrmion phases and phase dynamics in MnSi, highlighting effects of polycrystallinity.

Findings

Skyrmion lattice phase is averaged in polycrystal due to grain orientations.

Depinning field is stronger in polycrystal, affecting dissipative behavior.

Composite magnetoelectric method effectively probes topological phase dynamics.

Abstract

We have explored the skyrmion phases and phase diagram of poly and single-crystal MnSi by the measurements of the magnetoelectric coefficient alfaE and ac magnetic susceptibility of the MnSi/PMN-PT composite. We found that the regular skyrmion lattice phase in single crystal sample has been averaged in the MnSi polycrystal due to random grain orientations which results in an extended skyrmion lattice-conical mixture phase down to 25 K. The magnitude of the out-of-phase component in alfaE of the polycrystal, not single crystal, decreases gradually with decreasing frequency. With the changing of the driven ac field, it reveals a depinning threshold behavior in both samples. The depinning field is stronger in the polycrystal than that in single crystal and maybe responsible for the diminishing of dissipative behavior at lower frequency due to grain boundaries and defects. The composite magnetoelectric method provides a unique approach to probe topological phase dynamics.