Three-sublattice Skyrmion crystal in the antiferromagnetic triangular lattice

TL;DR

This paper demonstrates that a small Dzyaloshinskii-Moriya interaction in a frustrated antiferromagnetic triangular lattice induces a stable three-sublattice Skyrmion crystal phase, persisting at zero temperature, with distinct phase transitions characterized by topological order parameters.

Contribution

It reveals the formation of a three-sublattice antiferromagnetic Skyrmion crystal state induced by DM interactions, a novel finding in antiferromagnetic triangular lattices.

Findings

Small DM interactions induce AF-SkX formation.

AF-SkX consists of three interpenetrating Skyrmion crystals.

Phase transitions are characterized by topological order parameter jumps.

Abstract

The frustrated classical antiferromagnetic Heisenberg model with Dzyaloshinskii-Moriya (DM) interactions on the triangular lattice is studied under a magnetic field by means of semiclassical calculations and large-scale Monte Carlo simulations. We show that even a small DM interaction induces the formation of an Antiferromagnetic Skyrmion crystal (AF-SkX) state. Unlike what is observed in ferromagnetic materials, we show that the AF-SkX state consists of three interpenetrating Skyrmion crystals (one by sublattice), and most importantly, the AF-SkX state seems to survive in the limit of zero temperature. To characterize the phase diagram we compute the average of the topological order parameter which can be associated to the number of topological charges or Skyrmions. As the magnetic field increases this parameter presents a clear jump, indicating a discontinuous transition from a spiral phase into the AF-SkX phase, where multiple Bragg peaks coexist in the spin structure factor. For higher fields, a second (probably continuous) transition occurs into a featureless paramagnetic phase.