Surface magnetism in Fe3GeTe2 van der Waals ferromagnet

The surface magnetization of Fe3GeTe2 was examined by low-energy electron microscopy (LEEM) using an off-normal incidence electron beam. We found that the 180 degrees domain walls are of Bloch type. Temperature-dependent LEEM measurements yield a surface magnetization with a surface critical exponent beta 1 = 0.79 +/- 0.02. This result is consistent with surface magnetism in the 3D semi-infinite Heisenberg (beta 1 = 0.84 +/- 0.01) or Ising (beta 1 = 0.78 +/- 0.02) models, which is distinctly different from the bulk exponent (beta = 0.34 +/- 0.07). The measurements reveal the power of LEEM with a tilted beam to determine magnetic domain structure in quantum materials without the need for the use of spin-polarized electrons. Single crystal diffraction measurements reveal inversion symmetry-breaking weak peaks and yield space group P-6m2. This Fe site defect-derived loss of inversion symmetry enables the formation of skyrmions in this Fe3GeTe2 crystal.