Magnetic And Magneto-optical Studies Of Low-dimensional Materials

The successful isolation of grapheme from graphite has triggered experimental and theoretical studies on two-dimensional?2D?materials.For future nanoelectronic applications,the focus of research in two-dimensional materials is gradually moved from graphene to semiconducting two-dimensional materials and then 2D intrinsic magnetic materials.In this paper,the introduction part gives an overview of 2D materials and magneto-optic research on 2D materials.In the first section,the physical properties and application of graphene,2D semiconductor and 2D magnetic semiconductor are introduced.Then the magneto-optic measurements and the application of the magneto-optic measurements on 2D materials are introduced.The third section is the research motivation and research content of this work.The second chapter is the study of the Zeeman splitting of bulk 2H-MoTe₂ single crystal in high magnetic field,High magnetic field magneto-optical spectrum is utilized to study the A exciton of bulk 2H-MoTe₂ single crystal.A clear Zeeman splitting of the A exciton is observed under high magnetic fields up to 41.68 T,and the g-factor?-2.09± 0.08?is deduced.Moreover,high magnetic field enables us to obtain the quadratic diamagnetic shifts of the A exciton?0.486 ?eV T-2?.Accordingly,the reduced mass,binding energy,and reduced radius of the A exciton were obtained by using both two and three dimensional models.In the third chapter,the effects of hydrostatic pressure on spin-lattice coupling in two-dimensional ferromagnetic Cr₂Ge₂Te₆ are presented.First,we performed Raman spectra measurements of a 2DMS Cr₂Ge₂Te₆ under pressure.The Raman modes Eg3 and A gl show increase with the application of external pressure.Then we take magnetization measurements and the results show that the magnetic phase transition temperature Tc decreases from 66.6 K to 60.6 K?⁹%?as the pressure increases from 0 to 1 GPa.We also simulated the evolution of lattices thorough first principles calculations and found that the bond length of Cr-Cr decreases and the angle of Cr-Te-Cr diverges from 90°.The bond length decrease induced the increase of antiferromagneitic exchange interaction while the angle of Cr-Te-Cr diverges from 90°means the decrease of ferromagneitic exchange interaction.In conclusion,we found that these pressure effects could modulate the magnetic property of Cr₂Ge₂Te₆ and we also reveal the detailed information about the lattice deformation effect on the magnetic properties in Cr₂Ge₂Te₆.In the forth chapter,a time-resolved magneto-optical Kerr effect measurement?TR-MOKE?system is established.Firstly the detection principle of TR-MOKE measurement are introduced.And we solved some questions such as the weak signal collection.Then we acquired a TR-MOKE system with hundreds femtosecond resolution and 0-8 T,8-300 K detecting capability.Finally,the ultrafast spin relaxation of Cr₂Ge₂Te₆ is detected with this system.The fifth chapter is the summary and prospect of this work.In the next step the magnetic properties of Cr₂Ge₂Te₆ in higher pressure will be studied and the spin relaxation time of Cr₂Ge₂Te₆ will be detected using the home-made TR-MOKE system.