Skyrmion lattices in metallic and semiconducting B20 transition metal compounds

Abstract

High pressure studies in MnSi suggest the existence of a non-Fermi liquid state without quantum criticality. The observation of partial magnetic order in a small pocket of the pressure versus temperature phase diagram of MnSi has additionally inspired several proposals of complex spin textures in chiral magnets. We used neutron scattering to observe the formation of a two-dimensional lattice of skyrmion lines, a type of magnetic vortices, under applied magnetic fields in metallic and semiconducting B20 compounds. In strongly disordered systems the skyrmion lattice is hysteretic and extends over a large temperature range. Our study experimentally establishes magnetic materials lacking inversion symmetry as an arena for new forms of spin order composed of topologically stable spin textures.

Interplay between topological and thermodynamic stability in a metastable magnetic skyrmion lattice

“…Figure 3b summarizes the τ values derived for various temperatures. Note that as the temperature approaches the SkL transition temperature of 27 K, the relaxation time decreases dramatically and will likely decrease to less than 10 s. This behaviour reasonably accounts for why the SkL is readily annihilated during cooling in nominally clean systems, even though it is topologically stable 5,7,[10][11][12][13][14] . Nevertheless, after quickly passing through the high-temperature region in which the metastable SkL is short-lived, the lifetime becomes unmeasurably long toward low temperatures.…”

“…To address this issue, the lifetime of a metastable SkL requires investigation. In reality, however, unless randomly positioned dopant atoms 6 or pressure inhomogeneities 17 are introduced, the SkL in various chiral magnets is readily annihilated when the SkL becomes thermodynamically costly by passing through the SkL-to-conical transition line 5,7,[10][11][12][13][14] (for a typical phase diagram, see Fig. 2a).…”

Quantum fluctuations stabilize skyrmion textures

“…In addition, skyrmions display several features that are convenient from the viewpoint of potential applications, such as dimensions within the nanometric scale, topological protection, and high mobility. They have been observed in bulk magnets MnSi [5][6][7], Fe 1−x Co x Si [8,9,16,17], Mn 1−x Fe x Ge [18], and FeGe [19] using neutron scattering and Lorentz transmission electron microscopy. As it was reported, in these systems an external magnetic field can induce skyrmions with diameters of about a few tens of nanometers.…”

Specific features of magnetic phase diagram of an MnSi helimagnet

“…Nevertheless, in a number of earlier and recent publications (see, e.g., [2,[6][7][8][9][10][11][12][13][14][15][16][17]), the feature under consideration has been attributed not only to the reorientation of magnetic domains, but also to a tran sition from the helical to conical magnetic structure. We think that this treatment is incorrect.…”

“…What is wrong with this interpretation rather widely used in the literature [6][7][8][9][10][11][12][13][14][15][16][17]? In fact, this interpreta tion clearly contradicts the well known linear field dependence of MnSi magnetization observed starting with the smallest H values (see, e.g., early data [18] on MnSi magnetization).…”