Exotic skyrmion crystals in chiral magnets with compass anisotropy.

J P Chen,J -M Liu,Dan-Wei Zhang

doi:10.1038/srep29126

Abstract

The compass-type anisotropy appears naturally in diverse physical contexts with strong spin-orbit coupling (SOC) such as transition metal oxides and cold atomic gases etc, and it has been receiving substantial attention. Motivated by recent studies and particularly recent experimental observations on helimagnet MnGe, we investigate the critical roles of this compass-type anisotropy in modulating various spin textures of chiral magnets with strong SOC, by Monte Carlo simulations based on a classical Heisenberg spin model with Dzyaloshinsky-Moriya interaction and compass anisotropy. A phase diagram with emergent spin orders in the space of compass anisotropy and out-of-plane magnetic field is presented. In this phase diagram, we propose that a hybrid super-crystal structure consisting of alternating half-skyrmion and half-anti-skyrmion is the possible zero-field ground state of MnGe. The simulated evolution of the spin structure driven by magnetic field is in good accordance with experimental observations on MnGe. Therefore, this Heisenberg spin model successfully captures the main physics responsible for the magnetic structures in MnGe, and the present work may also be instructive to research on the magnetic states in other systems with strong SOC.

Highlights

The compass-type anisotropy appears naturally in diverse physical contexts with strong spin-orbit coupling (SOC) such as transition metal oxides and cold atomic gases etc, and it has been receiving substantial attention
Motivated by recent studies and recent experimental observations on helimagnet MnGe, we investigate the critical roles of this compass-type anisotropy in modulating various spin textures of chiral magnets with strong SOC, by Monte Carlo simulations based on a classical Heisenberg spin model with Dzyaloshinsky-Moriya interaction and compass anisotropy
We propose that a hybrid super-crystal structure consisting of alternating half-skyrmion and half-anti-skyrmion is the possible zero-field ground state of MnGe

Summary

OPEN Exotic skyrmion crystals in chiral magnets with compass anisotropy

The roles of magnetic anisotropies are usually delicate but substantial in determining the magnetic ground states in some cases These anisotropy terms are the weakest in energy scale among the above mentioned interactions, and the favored directions of helical spin orders are materials-dependent. This uniaxial anisotropy arises from the single-ion or dipolar shape anisotropy, and can be either an easy-axis (As < 0) or hard-axis (As > 0) anisotropy[27] To this stage, the effective anisotropy in these materials is governed by A =Ac +As. In some cases, the uniaxial anisotropy is vanished or much smaller than the compass term, which is typically true in MnGe and those magnetic systems with strong SOC mentioned above[15,16].

Results

Methods

Additional Information