Synthesis And Raman Spectroscopy Studies On Hexagonal-honeycomb Structural(quasi-)two-dimensional Magnetic Materials

Condensed matter physics is a discipline that studies the physical property and microstructure of condensed matter,and the interaction among them.Searching for the novel states of matter and understanding their physical mechanism are very important in the field of condensed matter physics.In recent years,discovery of intrinsic 2D ferromagnetic,antiferromagnetic,and(quasi-)2D QSL state greatly expanded the field of condensed matter physics.Among them,(quasi-)2D magnetic materials with hexagonal honeycomb structure have attracted a great deal of attention because of the rich physical connotation and great application potentials in the area of magnetic storages and spintronics.Raman spectroscopy is a non-invasive and convenient characterization tool.Not only the vibrational modes but also magnetic excitations can be detected by Raman spectra of materials.Combined Raman spectra with other measuring techniques and theoretical calculation,basic physical properties and magnetic properties of materials can be understood in depth.Furthermore,the sample preparation for Raman measurement is simple and the size of the samples can be down to single atomic layer and a few microns in lateral dimension.Therefore,Raman spectroscopy is a good technique to study(quasi-)2D magnetic materials.Here,we synthesized materials needed and used Raman spectroscopy to study the structural phase transition,magnetic excitations and orbital fluctuations in 2D magnetic materials?-Ti Br₃crystal,Cr Br₃crystal and quasi-2D QSL candidate material H₃Li Ir₂O₆crystals.At first,we synthesized?-Ti Br₃and Cr Br₃crystals by chemical vapor transportation(CVT)method,and prepared applicable samples for Raman measurement by dry transfer technique.Secondly,we synthesized high-quality?-Li₂Ir O₃crystal by high-temperature synthesis,then synthesized millimetre-sized H₃Li Ir₂O₆crystal by a soft chemical replacement of Li⁺with H⁺.We found that different products are obtained depend on different duration of chemical reaction,and optical pictures and scanning electron microscopy(SEM)patterns can be used to distinguish them preliminarily.At last,pyramidal H₃Li Ir₂O₆crystals were identified as high-quality H₃Li Ir₂O₆crystals.The measurement of basic property and Raman spectra of?-Ti Br₃crystal has been designed and investigated.In the section of?-Ti Br₃,we first identified the structural phase transition temperature at about 180 K with increase of interlayer spacing by temperature dependent X-ray diffraction(XRD)and specific heat measurements,then we found the magnetic collapse below the phase transition temperatures by measurement of magnetic susceptibility.Secondly,we carried out the temperature dependence of transmission electron microscopy(TEM)measurement,and we found the small variation of Ti-Ti distance.At last,temperature and polarization dependence of the Raman spectra of?-Ti Br₃crystal were carried out,and a tremendous frequency blue-shift and peak width narrowing were observed in the vibrational mode associated with Ti in-plane relative movement,which indicates the formation of Ti-Ti bond and dynamic Jahn-Teller freezing at low temperatures.We believe the interplay between orbital and lattice degree of freedoms plays a dominant role.The measurement of basic property,Raman and photoluminescence(PL)spectra of Cr Br₃crystal has been designed and investigated.In the section of Cr Br₃,the crystal samples were characterized by temperature dependent XRD and specific heat measurements,then we carried out the pressure dependence of Raman spectra measurement,and found two phase transition at about 6.66 GPa and 13.15 GPa.In addition,we carried out the pressure dependence of PL spectra measurement,and found the PL intensity reduced sharply at 6.66 GPa and a unusually peak position shift at 13.15 GPa.On the basis of analysis,we proposed that two transitions at about 6.66 GPa and 13.15 GPa are isostructural phase transition and electronic phase transition,respectively.The detailed physical nature of these phase transitions still need further study.The measurement of basic property and Raman spectra of H₃Li Ir₂O₆crystal has been designed and investigated.In the section of H₃Li Ir₂O₆studies,X-ray photoelectron spectroscopy(XPS)and XRD were first used to distinguish different products and determine the chemical formulas,and relatively accurate duration of chemical reaction was determined by XRD,magnetic susceptibility,specific heat and Raman measurements.Then,temperature and polarization dependence of the Raman spectra of high-quality H₃Li Ir₂O₆crystals were measured.During the processing the data of Raman spectra,a new universal method of temperature-calibration was proposed,and we found broadening phonons were caused by hydrogen randomness in this material,we mainly studied the dynamical Raman susceptibility and found that two-spin process dominated the magnetic Raman scattering,and the magnetic Raman continuum was originated from the fractionalized fermionic Majorana excitations.