Complex magnetism in 2D van der Waals magnets

Abstract

Two-dimensional van der Waals magnets are a promising platform for spintronics, yet their magnetic states remain incompletely understood, especially their sensitivity to subtle structural variations. This thesis maps that sensitivity in the FeₓGeTe₂ family by comparing Fe₅GeTe₂ and Fe₃GeTe₂. Using X-ray diffraction, Lorentz TEM, magnetic force microscopy, AC Kerr microscopy and magnetometry, with modelling, we link symmetry breaking and disorder to emergent complex magnetism. In Fe₅GeTe₂, inversion-symmetry breaking is weak and the Dzyaloshinskii-Moriya interaction (DMI) is negligible; field-stabilised textures appear as unconventional, non-chiral type-I and type-II magnetic bubbles. In contrast, Fe₃GeTe₂ shows sufficient structure-driven DMI to stabilise Néel-type skyrmions, and Fe disorder in the van der Waals gap produces a two-dimensional spin-glass state. These results connect structure to function and outline routes to engineer skyrmions and glassy magnetism in 2D materials.