Two-dimensional Fe3GeTe2: strain effect on magneto-crystalline anisotropy
- In recent years, two-dimensional (2D) materials have attracted growing attention. Atomically
thin materials exhibit remarkably different properties from bulk. According to Mermin-WagnerHohenberg theorem, no long-range magnetic order is possible in 2D. However, magnetism in 2D has
been recently observed experimentally such as CrI3, Cr2Ge2Te6 and Fe3GeTe2. Fe3GeTe2 has relatively
higher curie temperature ~130 K than other 2D materials. In this dissertation, we studied monolayer
and bilayer Fe3GeTe2, more specifically strain (−5 % ≤ η ≤ 5 %) effect on magnetic properties.
1. Monolayer Fe3GeTe2: Strain dependence of magnetism is revealed. Among two Fe sites,
Fe1 shows greater change of magnetic moments more than Fe2, from 1.53 𝜇𝐵 at −5 %
to 2.37 𝜇𝐵 at +5 % of strain. Density of states of Fe1 are compared for each strain,
different magnetic moments are associated with different peak feature. Furthermore,
magneto-crystalline anisotropy (MCA) is investigated, where monolayer Fe3GeTe2
prefers perpendicular magnetization for all strains. MCA energy changes with respect to
strain, where minimum value is 0.85 meV at η = −5 %, maximum value is 4.72 meV
without strain. Band structures at η = −5 % and 0 % are compared to analyze MCA of
2. Bilayer Fe3GeTe2: With ferromagnetic monolayer, bilayer Fe3GeTe2 energetically
prefers antiferromagnetic state without strain. Transition to ferromagnetic state occurs at
η = +4.16 %. Besides, at compressive strain, buckling happens in Fe2-Ge plane, which
results in different magnetic moments of Fe1(in) and Fe1(out). Density of states of Fe1
are investigated to study strain dependence of magnetic moments.
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