Surface Magnetism in Fe${}_3$GeTe${}_2$ Crystals

Abstract

The surface magnetization of Fe${}_3$GeTe${}_2$ was examined by low-energy electron microscopy (LEEM) using an off-normal incidence electron beam. We found that the 180${}^o$ domain walls are of Bloch type. Temperature-dependent LEEM measurements yield a surface magnetization with a surface critical exponent ${\hat{I}}^2$1 = 0.79 +/- 0.02. This result is consistent with surface magnetism in the 3D semi-infinite Heisenberg (${\hat{I}}^2$1 = 0.84 +/- 0.01) or Ising (${\hat{I}}^2$1 = 0.78 +/- 0.02) models, which is distinctly different from the bulk exponent (${\hat{I}}^2$ = 0.34 +/- 0.07). The measurements reveal the power of LEEM with a tilted beam to determine magnetic domain structure in quantum materials. 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 Fe${}_3$GeTe${}_2$ crystal.