Giant enhancement of the skyrmion stability in a chemically strained helimagnet

TL;DR

This study demonstrates that chemical strain in MnSi significantly stabilizes magnetic skyrmion lattices at low temperatures, far below the Curie point, using neutron scattering to reveal a robust topological magnetic phase.

Contribution

It shows that uniaxial lattice strain in MnSi stabilizes skyrmion lattices at low temperatures, expanding the conditions for their thermodynamic stability beyond previous narrow phase regions.

Findings

Skyrmion lattice stabilized at temperatures as low as 5 K.

Uniaxial strain enhances skyrmion stability in bulk MnSi.

Skyrmions are stable over conical spin spirals under strain.

Abstract

We employed small-angle neutron scattering to demonstrate that the magnetic skyrmion lattice can be realized in bulk chiral magnets as a thermodynamically stable state at temperatures much lower than the ordering temperature of the material. This is in the regime where temperature fluctuations become completely irrelevant to the formation of the topologically non-trivial magnetic texture. In this attempt we focused on the model helimagnet MnSi, in which the skyrmion lattice was previously well characterized and shown to exist only in a very narrow phase pocket close to the Curie temperature of 29.5~K. We revealed that large uniaxial distortions caused by the crystal-lattice strain in MnSi result in stabilization of the skyrmion lattice in magnetic fields applied perpendicular to the uniaxial strain at temperatures as low as 5~K. To study the bulk chiral magnet subjected to a large uniaxial stress, we have utilized $\mu$m-sized single-crystalline inclusions of MnSi naturally found inside single crystals of the nonmagnetic material Mn$_{11}$Si$_{19}$. The reciprocal-space imaging allowed us to unambiguously identify the stabilization of the skyrmion state over the competing conical spin spiral.