Field-induced pseudo-skyrmion phase in the antiferromagnetic kagome lattice

Abstract

We study the effects of an in-plane Dzyaloshinskii-Moriya interaction under an external magnetic field in the highly frustrated kagome antiferromagnet. We focus on the low-temperature phase diagram, which we obtain through extensive Monte-Carlo simulations. We show that, given the geometric frustration of the lattice, highly non trivial phases emerge. At low fields, lowering the temperature from a cooperative paramagnet phase, the kagome elementary plaquettes form non-coplanar arrangements with non-zero chirality, retaining a partial degeneracy. As the field increases, there is a transition from this "locally chiral phase" to an interpenetrated spiral phase with broken ${\mathcal{Z}}_3$ symmetry. Furthermore, we identify a quasi-skyrmion phase in a large portion of the magnetic phase diagram, which we characterize with a topological order parameter, the scalar chirality by triangular sublattice. This pseudo-skyrmion phase (pSkX) consists of a crystal arrangement of three interpenetrated non-Bravais lattices of skyrmion-like textures, but with a non-(fully)-polarized core. The edges of these pseudo-skyrmions remain polarized with the field, as the cores are progressively canted. Results show that this pseudo-skyrmion phase is stable up to the lowest simulated temperatures, and for a broad range of magnetic fields.

9 pages, 10 figures