Meron-antimeron crystals in noncentrosymmetric itinerant magnets on a triangular lattice

TL;DR

This paper theoretically predicts the stabilization of meron-antimeron crystal states in noncentrosymmetric itinerant magnets on a triangular lattice, revealing their field-dependent transformations and potential for experimental observation.

Contribution

It introduces the concept of meron-antimeron crystals in itinerant magnets and demonstrates their stabilization via simulated annealing considering specific interactions.

Findings

Rectangular and triangular MAXs are stabilized by spin-charge and spin-orbit interactions.

Triangular MAX transforms into skyrmion crystal under certain magnetic fields.

Highly anisotropic magnetic responses are observed depending on field direction.

Abstract

Multiple-$Q$ magnetic states often induce nontrivial topological spin textures, such as a skyrmion and a hedgehog. We theoretically investigate yet another multiple-$Q$ state with topological defects, a meron-antimeron crystal (MAX), represented by a periodic array of the meron and antimeron with a half-integer skyrmion number. Performing simulated annealing for an effective spin model of noncentrosymmetric itinerant magnets on a triangular lattice, we show that rectangular-shaped and triangular-shaped MAXs are stabilized by the interplay between the biquadratic interaction arising from the spin-charge coupling and the Dzyaloshinskii-Moriya interaction arising from the spin-orbit coupling. We also discuss the effect of a magnetic field on the triangular MAX, where highly anisotropic responses against a field direction are found. In particular, we show that the triangular MAX turns into the skyrmion crystal for the fields along the $y$ and $z$ directions, while it is replaced by another chiral state for the field along the $x$ direction. These results would inspire further experimental investigation of the MAXs in itinerant magnets.