Element-specific soft X-ray spectroscopy, scattering and imaging studies of skyrmion-hosting compound Co$_8$Zn$_8$Mn$_4$

Abstract

A room-temperature skyrmion-hosting compound Co$_8$Zn$_8$Mn$_4$ has been examined by means of soft X-ray absorption spectroscopy, resonant small-angle scattering and extended reference holography. An element-selective study was performed by exciting the $2p$-to-$3d$ transitions near Co and Mn $L_{2,3}$ absorption edges. By utilizing the coherence of soft X-ray beams the element-specific real-space distribution of local magnetization at different temperatures has been reconstructed using iterative phase retrieval and holography with extended reference. It was shown that the magnetic moments of Co and Mn are ferromagnetically coupled and exhibit similar magnetic patterns. Both imaging methods provide a real-space resolution of 30 nm and allowed to record a magnetic texture in the temperature range between $T\,=\,20$ K and $T\,=120\,$ K, demonstrating the elongation of the skyrmions along the principal crystallographic axes at low temperatures. Micromagnetic simulations have shown that such deformation is driven by decreasing ratio of symmetric exchange interaction to antisymmetric Dzyaloshinskii-Moriya interaction in the system and effect of the cubic anisotropy.