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

TL;DR

This study uses low-energy electron microscopy to analyze surface magnetism in Fe$_3$GeTe$_2$, revealing Bloch domain walls, surface critical behavior consistent with 3D models, and the presence of skyrmions due to inversion symmetry breaking.

Contribution

First detailed LEEM analysis of surface magnetism in Fe$_3$GeTe$_2$, identifying domain wall types, critical exponents, and symmetry-breaking effects enabling skyrmion formation.

Findings

Surface domain walls are of Bloch type.

Surface critical exponent matches 3D Heisenberg/Ising models.

Inversion symmetry-breaking enables skyrmion formation.

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 $\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. 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.