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

Abstract

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.

Néel-type skyrmions and their current-induced motion in van der Waals ferromagnet-based heterostructures

“…S9b [30]. We would also like to note that this result of nonexisting interfacial DMI in FGT bulk crystal has also been reported recently by Laref et al [60], opposing another work by Wang et al [24] that estimates some finite DMI within FGT.…”

“…Once established, by taking advantages of other 2D crystals that are stackable and offer unique electrical properties [1,2], this material platform could provide a different route towards skyrmion-based devices that have been challenging with conventional metallic ferromagnets [20,21]. Recently, skyrmionlike spin textures have been observed experimentally in exfoliated vdW ferromagnet materials (e.g., FGT and Cr 2 Ge 2 Te 6 ) and their heterostructures with the magnetic fields [22][23][24][25][26]. However, both Bloch-type and Néel-type skyrmions of the previous results have still been a subject of controversy.…”

Tunable Néel–Bloch Magnetic Twists in Fe3GeTe2 with van der Waals Structure

“…[3][4][5][6][7][8][9][10] As theoretically predicted, typical Bloch-type bubbles appear in centrosymmetric ferromagnets (FM) with magnetic dipolar interaction while Néel-type skyrmions are favored in thin heterostructure heavy metal/ FM with interfacial DMI. [8,9,[11][12][13] Several experimental observations support such theoretical predictions: Bloch-type bubbles, stabilized by the magnetic dipolar interaction in centrosymmetric FM, were claimed in the (001) thin plates (thinned from a bulk magnet) of vdW magnets Cr 2 Ge 2 Te 6 [4] and FGT, [5,8] while Néel-type skyrmions were reported in a heterostructure WTe 2 /FGT with an estimated large interfacial DMI strength of 1.0 mJ m −2 at the interface, much larger than their calculated critical DMI value of ≈0.1 mJ m −2 necessary for stabilizing Néel-type twists including skyrmions and domain walls. [6] The stability of Néeltype skyrmions is also predicted in multilayered films, such as the Pt/oxidized-FGT/FGT [9] and FGT/[Co/Pd] n .…”

“…To identify the Néel-or Bloch-type magnetic twists, researchers [3][4][5][6][7][8][9]14] attempt to use Lorentz transmission electron microscopy (TEM) observations while simultaneously tilting the thin sample: the Lorentz TEM images present magnetic contrast for Bloch-type twists, but monotonic intensity (no contrast) for Néel-type twists when the tilt angle is zero. Whereas magnetic contrast arises for the Néel-type twists upon nonzero sample tilt.…”

Tuning the Room Temperature Ferromagnetism in Fe5GeTe2 by Arsenic Substitution

“…skyrmions) is being heavily pursued in Fe 3−x GeTe 2 and related vdW heterostructures. [13,14,15,16,17] In general, Fe 5−x GeTe 2 and related Fe 4 GeTe 2 have garnered significant attention recently due to their high ordering temperature and complex behaviors. [18,19,20,21,22,23,24,25,26] The present work was motivated by identifying further routes to tune the magnetism in Fe 5−x GeTe 2 and related bulk phases so that novel properties and logical designs of het-erostructures can be achieved.…”