Frustration-driven magnetic fluctuations as the origin of the low-temperature skyrmion phase in Co7Zn7Mn6

Victor Ukleev ,H Luetkens,C N Wang,J S White,Y Taguchi,L Mangin-Thro,P M Derlet,Y Tokura,N Jaouen,Yuichi Yamasaki ,Kosuke Karube ,Taka‐Hisa Arima ,Akiko Kikkawa ,Yuichi Yokoyama ,Andrew Wildes ,Henrik M Rønnow ,Daichi Morikawa ,Cínthia Piamonteze ,Lili Yu ,Yusuke Tokunaga

doi:10.1038/s41535-021-00342-5

Abstract

In chiral cubic helimagnets, phases of magnetic skyrmions—topologically protected spin whirls—are stabilized by thermal fluctuations over a narrow region directly below the magnetic ordering temperature Tc. Due to often being touted for use in applications, there is a high demand to identify new ways to stabilize equilibrium skyrmion phases far below Tc where they may display an enhanced robustness against external perturbation due to a larger magnetic order parameter. Here, from quantum beam experiments on the chiral magnet Co7Zn7Mn6, we unveil a direct correlation between the stability of its second skyrmion phase-stable far from Tc, and a concomitant enhancement of an underlying magnetic fluctuation rate that is driven by geometric magnetic frustration. The influences of other leading skyrmion stability mechanisms, such as those derived from thermal fluctuations and low T cubic anisotropies, are shown to be weak in this system. We therefore advance the existence of a fundamental mechanism for stabilizing topological skyrmions in Co7Zn7Mn6 chiral magnet that draws upon magnetic frustration as the key ingredient.

Highlights

In non-centrosymmetric magnets, the interplay between ferromagnetic (FM) exchange, Dzyaloshinskii–Moriya interactions, and magnetic anisotropy, results in rich phase diagrams containing helical, conical and skyrmion lattice phases[1,2,3]
We find that the low-temperature skyrmion (LTSk) phase is stable over a thermal range characterized by an enhanced magnetic fluctuation rate on the μs time scale, the origin of which is connected to the geometric magnetic frustration of Mn moments on the 12d site
Muon spin relaxation experiments were performed to determine the H and T-dependent characteristic magnetic fluctuation rates in Co7Zn7Mn6. These experiments are sensitive to time scales ranging from 10−12 to 10−4 s depending on the size of the magnetic field at the muon site

Summary

Introduction

In non-centrosymmetric magnets, the interplay between ferromagnetic (FM) exchange, Dzyaloshinskii–Moriya interactions, and magnetic anisotropy, results in rich phase diagrams containing helical, conical and skyrmion lattice phases[1,2,3]. We find that the LTSk phase is stable over a thermal range characterized by an enhanced magnetic fluctuation rate on the μs time scale, the origin of which is connected to the geometric magnetic frustration of Mn moments on the 12d site.

Results

Conclusion