Possible skyrmion-lattice ground state in theB20chiral-lattice magnet MnGe as seen via small-angle neutron scattering

Abstract

We have investigated the magnetic structure in a polycrystalline sample of the B20-type MnGe by means of small-angle neutron scattering. On the projected diffraction plane normal to the incoming neutron beam, a Debye-ring-like pattern appears due to the random orientation of the spin helix q vectors (100). When an external magnetic field is applied normal to the incoming neutron beam, an intense peak with wave vector (q) perpendicular to the applied magnetic field is observed as the hallmark of the formation of a skyrmion lattice with a multiple-q helix in a wide temperature-magnetic-field region. This scattering intensity remains even after removing the magnetic field, which indicates that a skyrmion lattice is stabilized as the ground state. A different form of skyrmion lattice, either square or cubic, is proposed, which is also shown to be in good agreement with previous high-angle neutron diffraction results. Calculations based on such structures also describe the magnetic-field profile of the topological Hall resistivity.

Two-step pressure-induced collapse of magnetic order in the MnGe chiral magnet

“…The incommensurate wave vector k = (0,0,ζ ) parallel to a (001) axis levels off at a value of 0.167 below 30 K. It corresponds to the shortest helix pitch in the B20 series (29Å instead of 180Å in MnSi or 700Å in FeGe). A skyrmion lattice state was postulated based on resistivity and small angle neutron scattering on powder samples [14,18], but remains to be firmly established. High pressure experiments still need to be conducted, but ab initio calculations have predicted the band structure to evolve under pressure from strong band ferromagnetism via a half-metallic state towards a collapse of spin polarization [19].…”

Breathing modes of confined skyrmions in ultrathin magnetic dots

“…[1][2][3] Skyrmion states were predicted to appear in ultrathin films [4][5][6] and their observation in a variety of physical systems [7][8][9][10][11][12][13][14] has led to intense efforts to understand the physical conditions under which they are stable, along with their static and dynamic properties. Their topological nature has important consequences on electron and heat transport, 15,16 which lead to novel features involving current-driven dynamics of skyrmion lattices.…”

Towards control of the size and helicity of skyrmions in helimagnetic alloys by spin–orbit coupling

“…solid angle of 4π subtended by constituent spins, as characterized by a topological charge (skyrmion number) of −1. Skyrmions have a typical size of 3-100 nm and they tend to crystallize mostly in a hexagonal lattice form, or sometime in a tetragonal or cubic lattice form 10 ; we call such a magnetically ordered phase a skyrmion crystal (SkX). SkX was at first identified by a small-angle neutron diffraction study on B20- 16,17 .…”