Two-dimensional Fe3GeTe2: strain effect on magneto-crystalline anisotropy

Abstract

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 two strains. 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.