Experimental observation of chiral magnetic bobbers in B20-type FeGe

Abstract

Chiral magnetic skyrmions are nanoscale vortex-like spin textures that form in the presence of an applied magnetic field in ferromagnets that support the Dzyaloshinskii-Moriya interaction (DMI) because of strong spin-orbit coupling and broken inversion symmetry of the crystal. In sharp contrast to other systems that allow for the formation of a variety of two-dimensional (2D) skyrmions, in chiral magnets the presence of the DMI commonly prevents the stability and coexistence of topological excitations of different types . Recently, a new type of localized particle-like object-the chiral bobber (ChB)-was predicted theoretically in such materials . However, its existence has not yet been verified experimentally. Here, we report the direct observation of ChBs in thin films of B20-type FeGe by means of quantitative off-axis electron holography (EH). We identify the part of the temperature-magnetic field phase diagram in which ChBs exist and distinguish two mechanisms for their nucleation. Furthermore, we show that ChBs are able to coexist with skyrmions over a wide range of parameters, which suggests their possible practical applications in novel magnetic solid-state memory devices, in which a stream of binary data bits can be encoded by a sequence of skyrmions and bobbers.

Spin-resolved inelastic electron scattering by spin waves in noncollinear magnets

“…It could, for example, help to distinguish between a skyrmion tube and a magnetic bobber lattice in thin films [8]. These phases may have similar magnetic profiles at the very surface, but they differ deeper inside the film, which impacts on the spin waves.…”

“…They are noncollinear magnetic structures such as skyrmions, antiskyrmions, magnetic bobbers, and spin spirals [1][2][3][4][5][6][7][8]. These states arise from the delicate balance of internal and external interactions, such as the magnetic exchange, Dzyaloshinskii-Moriya and magnetic fields, which can trigger topologically nontrivial properties [9][10][11][12].…”

Helical magnetic structure and the anomalous and topological Hall effects in epitaxial B20 Fe1−yCoyGe films

“…[83]); (iii) grain boundary scattering at the boundaries of the chiral grains playing some role when the helix pitch is large compared to the lateral grain size; or (iv) the presence of exotic chiral spin textures in experiments which deviate significantly in their shape and properties from conventional skyrmions, which were taken as the foundation for the analysis of transport properties observed here. For example, there are a number of recent studies reporting the observation of so-called chiral bobbers [84,85] whose key feature is the presence of a singular Bloch point [86], and which could in principle exhibit transport properties radically different from those stemming from the adiabatic description.…”

Topological–chiral magnetic interactions driven by emergent orbital magnetism

“…We demonstrate that the interactions of the topological orbital moments with each other and with the spins form a new class of magnetic interactions − topological-chiral interactions − which can dominate over the Dzyaloshinskii-Moriya interaction, thus opening a path for realizing new classes of chiral magnetic materials with three-dimensional magnetization textures such as hopfions. Exotic magnetic textures with particle-like properties [1][2][3][4][5][6] offer great potential for innovative spintronic applications 7 and brain-inspired computing 8,9 . Magnetic skyrmions, twodimensional (2D) localized solitons, are a prominent realization of chiral spin structures, first observed in the material class of non-centrosymmetric B20 bulk compounds 1 .…”