Characteristics and temperature-field-thickness evolutions of magnetic domain structures in van der Waals magnet Fe3GeTe2 nanolayers

In two-dimensional van der Waals magnets, the presence of magnetic orders, strong spin-orbit coupling, and asymmetry at interfaces is the key ingredient for hosting noncollinear spin textures. Here, we investigate the characteristics and evolution of magnetic domain structures in thin Fe3GeTe2 nanolayers as a function of temperature, applied magnetic field, and specimen thickness using advanced magnetic electron microscopy. Specifically, electron holography analyses reveal the spin configurations of Bloch-type, zero-field-stabilized magnetic bubbles in 20-nm-thick Fe3GeTe2 nanolayers at cryogenic temperature. In situ Lorentz transmission electron microscopy measurements further provide detailed magnetic phase diagrams of noncollinear spin textures, including magnetic spirals and bubbles in Fe3GeTe2 as a function of temperature, applied magnetic field, and specimen thickness. We further estimate the micromagnetic parameters of Fe3GeTe2, such as anisotropy energy density and magnetization at specific specimen temperature using the critical thicknesses measured from Lorentz microscopy measurements. Our experimental results of magnetic domain structures in Fe3GeTe2 nanolayers reveal that due to their intrinsic highly uniaxial magnetocrystalline anisotropy, a very thin film of tens of nanometers of Fe3GeTe2 can support the spontaneous and stable formation of zero-field magnetic bubbles.