X-ray holographic imaging of magnetic surface spirals in FeGe lamellae

Abstract

Isotropic helimagnets are known to host a diverse range of chiral magnetic states. In 2016, Rybakov et al., theorized the presence of a surface-pinned stacked spin spiral phase [F. N. Rybakov et al., New J. Phys. 18, 045002 (2016)], which has yet to be observed experimentally. The phase is characterized by surface spiral periods exceeding the host material's fundamental winding period L D . Here, we present experimental evidence for the observation of this state in lamellae of FeGe using resonant x-ray holographic imaging data and micromagnetic simulations. We find images of FeGe lamellae, exceeding a critical thickness of 300 nm (4.3L D ), exhibit contrast modulations with a field-dependent periodicity of λ 1.4L D , consistent with theoretical predictions of the stacked spiral state. The identification of this spiral state has significant implications for the stability of other coexisting spin textures, and will help complete our understanding of helimagnetic systems.

Enhanced skyrmion metastability under applied strain in FeGe

“…In this study, we employ resonant x-ray holography [36,37] to image the real space magnetization [38] of metastable skyrmion states under the effects of thermally induced tensile strain on lamella of single crystal FeGe [39,40]. Through differential thermal contraction between the sample and substrate, we confirm elliptical skyrmion lattice deformation using small-angle x-ray scattering (SAXS) and demonstrate enhanced metasta- i zero-field-cooled (ZFC) protocol including cooling in zero-field to 240 K then increasing magnetic field to 100 mT (orange) and field-cooled protocol at 100 mT to 240 K with a reduction in magnetic field to 0 mT (green).…”

Enhanced skyrmion metastability under applied strain in FeGe

“…(j) Field-reversal protocol including a field cool at 100 mT to 100 K followed by a reversal of the magnetic field to −150 mT and back to 100 mT. skyrmion states under the effects of thermally induced tensile strain on lamellae of single crystal FeGe [39,40]. Through differential thermal contraction between the sample and the substrate, we confirm elliptical skyrmion lattice deformation using small-angle x-ray scattering (SAXS) and demonstrate enhanced metastability of the skyrmion lattice against helical reorientations [41][42][43] and magnetic field reversals.…”