Electrical Detection and Magnetic Imaging of Stabilized Magnetic Skyrmions in Fe_1−xCo_xGe (x < 0.1) Microplates

Abstract

Magnetic skyrmions are topologically protected spin textures that are being heavily investigated for their potential use in next generation magnetic storage devices.However, transport studies of skyrmions in nanostructures is limited due to the difficulty of their detection. Here, magnetic skyrmions and other magnetic phases in Fe 1-x Co x Ge (x < 0.1) microplates (MPLs) newly synthesized via chemical vapor deposition were studied using both magnetic imaging and transport measurements. Lorentz transmission electron This article is protected by copyright. All rights reserved.2 microscopy revealed a stabilized magnetic skyrmion phase near room temperature (~280 K) and a quenched metastable skyrmion lattice via field cooling. Magnetoresistance (MR) measurements in three different configurations revealed a unique anomalous MR signal at temperatures below 200 K and two distinct field dependent magnetic transitions. The topological Hall effect (THE), known as the electronic signature of magnetic skyrmion phase, was detected for the first time in a Fe 1-x Co x Ge nanostructure, with a large and positive peak THE resistivity of ~32 nΩ•cm at 260 K. This large magnitude is attributed to both nanostructuring and decreased carrier concentrations due to Co alloying of the Fe 1-x Co x Ge MPL, which suggests alloying as a strategy to enhance the THE signals of skyrmion materials. A consistent magnetic phase diagram summarized from both the magentic imaging and transport measurements shows that the magnetic skyrmions are stabilized in Fe 1-x Co x Ge MPLs compared to bulk materials. This comprehensive electrical device and magnetic imaging study lays the solid foundation for future studies of skyrmion-based nanodevices to realize their full potential in information storage and processing technologies.

In‐Plane Magnetic Field‐Driven Creation and Annihilation of Magnetic Skyrmion Strings in Nanostructures

“…Figure 1b shows MR– H || curves over selected temperatures in the range of 10 – 290 K. The field‐dependent MR signal disappears for the paramagnetic state measured above T c ≈ 280 K. Anomalous MR signature accompanied by appreciable hysteresis was observed at low temperatures (below ≈ 100 K) which is marked by a sharp change in the MR signal when | H || | is below the saturation field. Qualitatively similar low temperature MR features under H || were also observed (but not explained) in the FeGe NPL (with 3% Co doping) devices, [ 28 ] but not in FeGe bulk [ 31 ] and thin film systems, [ 32 ] which makes these anomalous MR features unique to nanostructures. The strong anisotropic response of MR signal obtained in the parallel MR configuration stands in clear contrast to the smooth MR curve in the perpendicular configuration (see a specific comparison at 10 K in Figure 1c), suggesting an in‐plane magnetic anisotropy.…”

Signatures of a Charge Density Wave Phase and the Chiral Anomaly in the Fermionic Material Cobalt Monosilicide CoSi

“…This also holds for CoSi . Interestingly, related silicides like MnSi, Fe 0.75 Co 0.25 Si and germanides like Fe 1 − x Co x Ge also feature skyrmion states.…”

“…In contrast, the fermionic materials host Weyl fermions that are degenerated and carry a higher chiral charge. [5,8,9] Interestingly, related silicides like MnSi, [10] Fe 0.75 Co 0.25 Si [11] and germanides like Fe 1 −x Co x Ge [12,13] also feature skyrmion states.In general, Weyl materials show characteristic quantum effects in the transport, resulting for example in quantum Materials with topological electronic states have emerged as one of the most exciting discoveries of condensed quantum matter, hosting quasiparticles with extremely low effective mass and high mobility. The chiral charge of the material strongly depends on the space group of the crystal structure.…”

“…CoSi has a cubic B20 crystal structure (space group 198 P2 1 3) with broken space inversion symmetry. [5,8,9] Interestingly, related silicides like MnSi, [10] Fe 0.75 Co 0.25 Si [11] and germanides like Fe 1 −x Co x Ge [12,13] also feature skyrmion states. [4] In CoSi, the Weyl fermions carry a chiral charge of up to ±4.…”

Phase Selection in Mn–Si Alloys by Fast Solid‐State Reaction with Enhanced Skyrmion Stability

“…Magnetic skyrmions are topologically protected spin configurations [ 1,2 ] and have been experimentally discovered in a series of magnetic compounds with noncentrosymmetric crystal structure, such as B20‐type transition‐metal silicides or germanides. [ 3–5 ] In those materials, the Dzyaloshinskii Moriya (DM) interaction and Heisenberg exchange interaction compete with each other, resulting in the formation of a whirling spin structure. The size of skyrmions or the associated magnetic modulation period is determined by the ratio between the magnitudes of the DM interaction and the ferromagnetic exchange interaction, and typically ranges from 1 to 100 nm.…”