The Structure And Magnetic Properties Of The Frustrated Triangular Lattice Antiferromagnetic Cs₂CuBr₄ And Cs₂CuCl₄ Under Stress

The triangular lattice antiferromagnetic frustration materials have many novel magnetic properties,such as quantum spin liquid?QSL?,1/3 saturation magnetic moment magnetization platform,which attracts great interests for a better understanding of the magnetic behavior and the magnetic ground state of magnetic frustration materials.In this thesis,we focus on two kinds of triangular lattice magnet frustration materials,Cs₂CuBr₄ and Cs₂CuCl₄,and investigate their structure and magnetic properties under high pressure and compare with the K⁺and Cl^-co-doped Cs₂CuBr₄.The main research contents are as follows:1.Cs₂CuBr₄,Cs₂CuCl₄ and Cs_2-xK_xCuBr_4-xCl_x single crystals are prepared by the slow evaporation of aqueous solutions.A pre-pressurized Cs₂CuBr₄ are prepared by a Hexa-orientation Press.2.A pressure induced phase transition is confirmed in Cs₂CuBr₄ around 5 GPa by the in-situ high-pressure Raman spectroscopy as well as the in-situ high-pressure X-ray diffraction.Below 5 GPa,the Cs₂CuBr₄ crystal maintains an orthorhombic structure with a space group Pnma.Above 5 GPa,the structure of Cs₂CuBr₄ crystal transforms to a monoclinic P2/m phase.3.The in-situ high pressure Raman spectroscopy of Cs₂CuCl₄ shows that the pressure-induced structural phase transition around 5 GPa,where the color of the sample changes from yellow?at low pressure?to orange?at high pressure?.Below 5 GPa,the Jahn-Teller effect in the CuCl₄ tetrahedron is suppressed as the pressure increases.4.The post-pressurized Cs₂CuBr₄ sample maintained an orthogonal structure.As the pressure increases,the lattice constants of the sample decrease,and the Curie-Weiss temperature(?_CW)increases.This result is consistent with that in the K⁺and Cl^-co-doped Cs_2-xK_xCuBr_4-xCl_x samples,where the lattice constants decrease with the increasing doping concentration,while the Curie-Weiss temperature increases.It is suggested that the reduce of the lattice constants leads to an increasement of the antiferromagnetic interaction inside the bc plane,an increasement of the Curie-Weiss temperature.