Topological stability of spin textures in Si/Co-doped helimagnet FeGe

Abstract

Element substitutions with magnetic or non-magnetic atoms are known to significantly impact the magnetic structure and related transport properties of magnets. To clarify the change of magnetic structure of B20-type magnets with element doping, we conduct real-space observations of spin textures and their temperature ( T )-magnetic field ( H ) phase diagrams of a helimagnet FeGe with partially substituting Fe and Ge with Co and Si, respectively. The helical period ( λ ) changes dramatically by the element doping: λ increases by 147% to 103 nm in 30% Co-doped FeGe, whereas it decreases by around 70% to 49 nm in 30% Si-doped FeGe, compared to the λ = 70 nm in FeGe. Upon applying the magnetic field normally to (001), (110), and (111) thin plates of both FeSi _0.3 Ge _0.7 and Fe _0.7 Co _0.3 Ge, the hexagonal skyrmion crystal (SkX) state emerges. The magnetic phase diagrams observed through the real-space imaging reveal that (1) the SkX can extend to a larger T-H window by reducing the sample thickness or by cooling the sample under specific magnetic fields from temperatures above the transition temperature ( T _C ); (2) the stability of the SkX phase differs between Si-doped and Co-doped FeGe: the SkX phase is most unstable in the (111) FeSi _0.3 Ge _0.7 , while it remains robust in the (111) Fe _0.7 Co _0.3 Ge. These differences indicate distinct anisotropic behavior in FeGe with magnetic (Co) and non-magnetic-element (Si) dopants.

Keywords

• magnetic skyrmion
• B20-type compound
• element substitution