  Van der Waals (vdW) magnetic materials such as Cr2Ge2Te6 (CGT) show promise
for novel memory and logic applications. This is due to their broadly tunable
magnetic properties and the presence of topological magnetic features such as
skyrmionic bubbles. A systematic study of thickness and oxidation effects on
magnetic domain structures is important for designing devices and vdW
heterostructures for practical applications. Here, we investigate thickness
effects on magnetic properties, magnetic domains, and bubbles in
oxidation-controlled CGT crystals. We find that CGT exposed to ambient
conditions for 5 days forms an oxide layer approximately 5 nm thick. This
oxidation leads to a significant increase in the oxidation state of the Cr
ions, indicating a change in local magnetic properties. This is supported by
real space magnetic texture imaging through Lorentz transmission electron
microscopy. By comparing the thickness dependent saturation field of oxidized
and pristine crystals, we find that oxidation leads to a non-magnetic surface
layer which is thicker than the oxide layer alone. We also find that the stripe
domain width and skyrmionic bubble size are strongly affected by the crystal
thickness in pristine crystals. These findings underscore the impact of
thickness and surface oxidation on the properties of CGT such as saturation
field and domain/skyrmionic bubble size and suggest a pathway for manipulating
magnetic properties through a controlled oxidation process.
