Chemical Pressure Stabilization of the Cubic B20 Structure in Skyrmion Hosting Fe_1–xCo_xGe Alloys

Abstract

Iron monogermanide (FeGe) with the noncentrosymmetric cubic B20 structure is a well-known helimagnet and a magnetic skyrmion host with a relatively high ordering temperature (∼280 K). FeGe and related metal monogermanide compounds, such as CoGe and MnGe, have several structural polymorphs and typically require high pressure (∼4 GPa) and high temperature (∼1000 °C) to synthesize in the cubic B20 structure. Here, we report that the cubic B20 phase of both FeGe and alloys of Fe 1−x Co x Ge could in fact be formed without the application of high pressure by simply reacting elemental powders at modest temperatures (550 °C). Furthermore, the incorporation of Co into Fe 1−x Co x Ge (0.05 ≤ x ≤ 0.1) stabilizes the cubic B20 structure up to 650 °C, which we propose is caused by chemical pressure induced by the incorporation of Co into the lattice. Interestingly, chemical vapor transport reactions using the Fe 1−x Co x Ge alloys as precursors yield plentiful growth of large (0.1 to 1 mm) single crystals of pure FeGe. Magnetic susceptibility measurements of the Fe 0.95 Co 0.05 Ge alloy show evidence of a skyrmion phase not previously reported in the Fe 1−x Co x Ge system.

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.…”

Magnetoentropic signatures of skyrmionic phase behavior in FeGe

“…More broadly, the continued unveiling of magnetic skyrmions in materials near and above room temperature and their potential uses in practical applications [20][21][22][23][24][25][26][27] has further highlighted the need to quantify the thermodynamically distinct spin states in their high temperature magnetic phase diagrams. New materials continue to be discovered, many with near-room-temperature skyrmion states [22,[28][29][30][31][32]. Precise and quantitative techniques for rapidly interpreting magnetic anomalies in this new realm of materials and for ultimately surveying thermodynamically distinct magnetic states in their phase diagrams are needed.…”

Data-driven design of B20 alloys with targeted magnetic properties guided by machine learning and density functional theory

“…This indicates the challenge and the low-throughput nature of the synthesis and characterization efforts in the materials discovery cycle. The low-throughput nature of data generation from experiments is justified by the need for performing expensive and time-consuming synthesis (sometimes requiring nonequilibrium processing routes [12,13]). Moreover, nontrivial characterization studies are also needed to reliably report the crystal structure and magnetic properties of these alloys, adding to the challenge.…”