Temperature-driven transition from skyrmion to bubble crystals in centrosymmetric itinerant magnets

Satoru Hayami

doi:10.1088/1367-2630/ac3683

Abstract

Interplay between itinerant electrons and localized spins in itinerant magnets gives rise to a variety of noncoplanar multiple-Q spin textures, such as the skyrmion, hedgehog, meron, and vortex. We elucidate that another type of multiple-Q state consisting of collinear sinusoidal waves, a magnetic bubble crystal, appears at finite temperatures in a centrosymmetric itinerant electron system. The results are obtained for the classical Kondo lattice model with easy-axis single-ion anisotropy on a triangular lattice by a large-scale numerical simulation. We find that a finite-temperature topological phase transition between the skyrmion crystal and the bubble crystal occurs by changing the temperature. We obtain the minimal key ingredients for inducing the finite-temperature transition by analyzing an effective spin model where it is shown that the synergy between the multiple-spin interaction and magnetic anisotropy plays a significant role.

Highlights

A magnetic skyrmion, which is characterized by a swirling spin texture to have a nontrivial topological number, has been extensively studied in condensed matter physics, as it exhibits a number of intriguing physical phenomena that arises from emergent magnetic fields, such as the topological Hall effect [1, 2, 3, 4]
Temperature-driven transition from skyrmion to bubble crystals in centrosymmetric itinerant magnets3 model with an easy-axis single-ion anisotropy on a triangular lattice and performing large-scale Langevin dynamics simulations combined with the kernel polynomial method (KPM-LD) [101], we find that the system exhibits a finite-temperature phase transition between the SkX described by the triple-Q spiral waves and the bubble crystal described by the triple-Q collinear sinusoidal waves
We show that such a finite-temperature phase transition between the SkX and the bubble crystal is captured by an effective spin model derived from the Kondo lattice model, suggseting that the interplay between the multiple-spin interactions and magnetic anisotropy is essential to the transition

Summary

Introduction

A magnetic skyrmion, which is characterized by a swirling spin texture to have a nontrivial topological (skyrmion) number, has been extensively studied in condensed matter physics, as it exhibits a number of intriguing physical phenomena that arises from emergent magnetic fields, such as the topological Hall effect [1, 2, 3, 4]. Temperature-driven transition from skyrmion to bubble crystals in centrosymmetric itinerant magnets model with an easy-axis single-ion anisotropy on a triangular lattice and performing large-scale Langevin dynamics simulations combined with the kernel polynomial method (KPM-LD) [101], we find that the system exhibits a finite-temperature phase transition between the SkX described by the triple-Q spiral waves and the bubble crystal described by the triple-Q collinear sinusoidal waves. This phase transition is regarded as the topological phase transition where the scalar chirality is turned on and off. Our results indicate that temperature fluctuations can be a source of multiple-Q states and drive a further topological phase transition in the skyrmion-hosting itinerant magnets

Classical Kondo lattice model

Effective spin model

Summary