Simulation of Two-dimensional Magnetic Material and Strain Engineering Method

Abstract

This thesis investigates the magnetic properties and strain tunability of two-dimensional magnetic materials using Density Functional Theory (DFT), along with theoretical and numerical methods. In Chapter 1, I introduce the formalism of DFT and its application to spin-polarized systems. Chapter 2 focuses on a two-dimensional Van der Waals heterostructure, formed by stacking monolayer antiferromagnetic MnPSe₃ with monolayer WSe₂, to explore strain-modulated topological spin textures. DFT calculations are employed to examine their stacking configurations and electronic structure, while a continuum model is used to simulate strain formation in the heterostructure. The strain field is subsequently applied to simulate the formation of strain-modulated spin textures, driven by the magnetoelastic coupling effect. The results reveal that while MnPSe₃ exhibits strain-tunability, its strong exchange coupling inhibits the formation of vortex spin textures.This limitation motivates the work in Chapter 3, where I explore the magnetic properties of the strain-tunable itinerant ferromagnets Fe₃GeTe₂ and Fe₄GeTe₂. Monolayer Fe₃GeTe₂ and Fe₄GeTe₂ are found to possess significant magnetoelastic coupling, with distinct magnetic anisotropies: Fe₃GeTe₂ shows strong perpendicular anisotropy, while Fe₄GeTe₂ exhibits in-plane anisotropy. An ab initio tight-binding model is constructed for both materials, and perturbation theory is used to analyze the contribution of spin-orbit coupling to their magnetic anisotropy. Finally, in Chapter 4, I introduce the twisted CrI₃ magnetic system and propose a novel autocorrelation analysis, leading to the first discovery of Moiré magnetism.