Synthesis,Characterization,and Magnetism Of Two-Dimensional FeTe₂ Nanosheets

In the past few decades,many innovative physical phenomena have been discovered in magnetic thin films,and there are many potentially valuable applications.The recent discovery of monolayer two-dimensional（2D）magnetic material has attracted widespread attention.2D magnetic materials will serve as a good carrier for studying 2D magnetic mechanisms,spintronics,and exploring new magnetic applications.At the same time,this discovery has also promoted the rapid development of many 2D magnetic crystals and magnetic applications,but there is still a lack of high Curie temperature van der Waals ferromagnets in the family of 2D magnetic crystal.The discovery and preparation of high Curie temperature 2D van der Waals crystals will be the future development needs and direction.In this context,this article discovered a new 2D magnetic crystal with high Curie temperature that has never been reported,and used first-principles calculations to study the magnetic mechanism.The research contents of this article include:（1）Preparation of 2D FeTe₂ single crystal nanosheets with high purity and good quality by chemical vapor deposition.The growth parameters of iron telluride nanosheets were optimized to obtain the best growth conditions for the synthesis of high-quality 2D FeTe₂ nanosheets.This work explores the growth mechanism of 2D FeTe₂ from the perspective of temperature,airflow and growth time.According to the material morphology of different stages,the growth model of FeTe₂ nanosheets was analyzed.（2）The elemental composition,proportion and valence state of FeTe₂ nanosheets were analyzed by spectroscopic characterization.Raman spectrometer was used to investigate the effect of geometry on the crystal quality and the thickness-dependent Raman response.The lattice parameters and structure of the synthesized FeTe₂ nanosheets were characterized by X-ray diffraction（XRD）and scanning transmission electron microscopy（STEM）.The physical property measurement system（PPMS）measured that the FeTe₂ nanosheets can produce a strong magnetism of about 5 emu/g under 1 Tesla magnetic field.（3）First-principles calculations are used to predict the structure of T-phase FeTe₂.Spin polarization calculations of monolayer,bilayer,trilayer,and bulk T-phase FeTe₂ were performed.The ferromagnetic and three types of antiferromagnetic configurations were set up and the density of states was plotted to analyze the magnetic behavior and magnetic generation mechanism of T-phase FeTe₂.The high Curie temperature of monolayer T-phase FeTe₂ is estimated to be 310K by Monte Carlo simulation based on Ising model.