Unpinning the skyrmion lattice in MnSi: Effect of substitutional disorder

Abstract

By employing magnetization and small angle neutron scattering (SANS) measurements, we have investigated the behavior of the skyrmion lattice (SKL) and the helical order in MnSi 0.992 Ga 0.008 . Our results indicate that the order of the SKL is sensitive to the orientation of an applied magnetic field with respect to the crystal lattice and to variations in the sequence of small temperature and applied magnetic field changes. The disorder caused by the substitution of the heavier element Ga for Si is sufficient to reduce the pinning of the SKL to the underlying crystalline lattice, reducing the propensity for the SKL to be aligned with the crystal lattice. This tendency is most evident when the applied field is not well oriented with respect to the high symmetry axes of the crystal resulting in disorder in the long range SKL while maintaining sharp short range (radial) order. We have also investigated the effect of substituting heavier elements into MnSi on the reorientation process of the helical domains with field cycling in MnSi 0.992 Ga 0.008 and Mn 0.985 Ir 0.015 Si. A comparison of the reorientation process in these materials with field reduction indicates that the substitution of heavier elements on either Mn or Si sites creates a higher energy barrier for the reorientation of the helical order and for the formation of domains.

Chiral Magnetism and High-Temperature Skyrmions in B20-Ordered Co-Si

“…5(a). χðHÞ exhibits an anomaly between the fields H A1 ¼ 0.14 and H A2 ¼ 0.32 kOe, similar to those observed for skyrmion spin structures in other systems [35][36][37][38][39][40][41][42][43][44][45]. Note that MðHÞ data in Fig.…”

“…As observed in other systems [3,[35][36][37][38][39][40][41][42][43][44][45], the skyrmion phase, green region in Fig. 5(b), is limited to a certain temperature range, between 285 and 305 K for x ¼ 0.043.…”

“…The chiral spin structure of B20 magnets is well known to support spin spirals (helices) [4] and skyrmions [1-3, 5,7]. Such noncollinear spin structures can be investigated by analyzing the field dependences of MðHÞ and χ ¼ dMðHÞ=dH, where they give rise to characteristic features or anomalies just below T c in single crystals, thin films and polycrystalline samples, corresponding to skyrmion spin structures [3,[35][36][37][38][39][40][41][42][43][44][45]. The room-temperature field dependences of M and χ for x ¼ 0.043 sample are shown in Fig.…”

Effects of interfacial Dzyaloshinskii–Moriya interaction on magnetic dynamics

“…The DMI can exist in MnSi and other specific B20 structured bulk materials [53][54][55][56][57][58][59], originating from the broken inversion symmetry of the crystal structure. Similarly, the DMI also occur at the HM/FM interface due to the asymmetry of the upper and lower surfaces of the ferromagnetic film, which is the so-called iDMI [48] (figure 1(b)).…”

Spin-disorder intervened avoidance of quantum criticality in B20 cubic Mn 1−xVx Si

“…Modifying magnetic materials through chemical substitution stands as a viable common approach to discovering novel phases, when compared to H and p applications. Chemical substitutions can induce positive or negative chemical pressures, depending on the atomic radii of the substituting elements [1][2][3][4][5][6][7].…”