Topological transitions among skyrmion- and hedgehog-lattice states in cubic chiral magnets

Y Fujishiro,K Ohishi,H Mitamura,T Nakajima,R Arita,K Kindo,A Miyake,K Akiba,T Arima,K Kakurai,N Kanazawa,M Tokunaga,A Matsuo,X Z Yu,T Koretsune,Y Kawamura,Y Tokura

doi:10.1038/s41467-019-08985-6

Abstract

Manipulating topological spin textures is a key for exploring unprecedented emergent electromagnetic phenomena. Whereas switching control of magnetic skyrmions, e.g., the transitions between a skyrmion-lattice phase and conventional magnetic orders, is intensively studied towards development of future memory device concepts, transitions among spin textures with different topological orders remain largely unexplored. Here we develop a series of chiral magnets MnSi1−xGex, serving as a platform for transitions among skyrmion- and hedgehog-lattice states. By neutron scattering, Lorentz transmission electron microscopy and high-field transport measurements, we observe three different topological spin textures with variation of the lattice constant controlled by Si/Ge substitution: two-dimensional skyrmion lattice in x = 0–0.25 and two distinct three-dimensional hedgehog lattices in x = 0.3–0.6 and x = 0.7–1. The emergence of various topological spin states in the chemical-pressure-controlled materials suggests a new route for direct manipulation of the spin-texture topology by facile mechanical methods.

Highlights

Manipulating topological spin textures is a key for exploring unprecedented emergent electromagnetic phenomena
In order to clarify the variation of magnetic period (λ) and direction of wavevectors (q-vectors) in MnSi1−xGex, small- and wide-angle neutron scattering experiments as well as Lorentz transmission electron microscopy (LTEM) observations were performed at zero magnetic field
The present results on the SANS and LTEM and on the topological Hall effects unveil the transitions among distinct topological spin textures, namely 2D skyrmion lattice (SkL) and two classes of 3D hedgehog lattice (HL) in cubic chiral magnets MnSi1−xGex

Summary

Introduction

Manipulating topological spin textures is a key for exploring unprecedented emergent electromagnetic phenomena. Lorentz transmission electron microscopy and high-field transport measurements, we observe three different topological spin textures with variation of the lattice constant controlled by Si/Ge substitution: two-dimensional skyrmion lattice in x = 0–0.25 and two distinct three-dimensional hedgehog lattices in x = 0.3–0.6 and x = 0.7–1. This quantity counts how many times the direction of the local magnetization, i.e., n(r) = m (r)/|m(r)|, wraps the unit sphere within the unit area S. When a magnetic structure possesses a non-zero integer winding number, it behaves as a topologically stable spin-object, producing emergent phenomena unique to its topological class. Through the interaction with conduction electrons, skyrmions generate the effective magnetic field confined in each interior, socalled emergenthmagnetic field ias defined by the Berry curvature bk

Methods

Results

Conclusion