Preparation And Electromagnetic Properties Of Layered Chalcogenide Oxide Sr₂IrO₄ Based On Lattice Modulation

Over the past decade,the importance of spin-orbit interactions in electronic structures has been gradually recognized with the discovery of many topological materials and 5d transition element compounds.Strong spin-orbit interactions in 5d transition metal oxides are capable of generating complex competition and balance on the energy scale with electron correlation and Hund coupling rules,inducing a range of more novel physical phenomena and effects.Electronic and magnetic materials made of 5d transition metal oxides are of great interest for their potential applications in spintronics and the modern electronics industry.Sr₂IrO₄,a typical 5d transition metal oxide,has a system in which the balance between Coulomb interactions,spin-orbit coupling and crystal field cleavage is easily disturbed.In addition,its crystal structure is extremely similar to that of the high-temperature superconducting parent material La₂CuO₄,therefore the system is considered as a candidate for exploring many novel physical properties and has become a hot research topic in the field of high-temperature superconductivity in recent years.In order to continue exploring more exotic physical properties in this system,this thesis investigates the correlation between electromagnetic physical mechanisms and structural by researching the doping effects on Sr₂IrO₄ compounds at the Sr site.The main elements are as follows:（1）Firstly,an overview of spin-orbit coupling is given to elucidate the formation mechanism of J_eff=1/2 Mott insulator.On this basis,a more comprehensive summary of previous research results on the basic physical and electromagnetic properties of Sr₂IrO₄ is presented.Finally,the main research of this thesis is led.（2）In this thesis,the doped samples Sr_2-xBi_xIrO₄（x=0,0.02,0.04,0.06,0.08）for the nonmagnetic ion Bi³⁺and Sr_2-xDy_xIrO₄（x=0,0.02,0.04,0.06）for the magnetic ion Dy³⁺were prepared by the conventional solid-phase reaction method,respectively.After a series of structural characterization by XRD,SEM,EDS,Raman and XPS.It is shown that both doped samples have good I4₁/acd space group structure of pure phase and more accurate elemental occupancy ratio.Fullprof refinement data indicate that the rotation and tetragonal distortion of the doped IrO₆ octahedra show non-monotonic changes,which may be related to the disorder of ions and lattice occupation.The lattice changes also profoundly affect the electrical and magnetic properties of the samples,and the UV spectra,electrical and magnetic properties of the successfully prepared samples were measured.The electrical data show that both dopings make the samples remain insulating at all times with a small energy gap E_g,indicating that all compounds are Mott insulators after doping;the magnetic data show that both dopings inhibit ferromagnetic interactions overall and lower the magnetic transition temperature,but the difference is that the doped samples exhibit a significant increase in magnetization at low temperatures because Dy³⁺is a magnetically charged ion.The non-monotonic variation of the resistivity and magnetic parameters is consistent with the variation of the lattice constants,indicating that the electrical and magnetic properties of both Bi and Dy doped systems are closely related to the rotational and tetragonal distortions of the IrO₆ octahedra,and there are structural,electrical,and magnetic coupling mechanisms in the samples.（3）LiInCr₄O₈ is an oxide with a respiring pyrochlore structure and the respiration factor can modulate its ground state magnetism.Therefore,in Chapter 5 of this dissertation,Mn doping of spinel oxide LiInCr₄O₈ with spin lattice interaction was also investigated to change the Cr-Cr bond length and thus the magnitude of the respiration factor to investigate the magnetic trends.Firstly,a series of structural characterization and physical property measurements of the doped LiInCr_4-xMn_xO₈（x=0,0.2,0.4,0.5）samples were carried out.It is obvious from the SEM images that the average grain size of the Mn-doped samples is smaller and the gaps between the grains are also smaller,indicating stronger intermolecular forces.The magnetic data show that the long-range antiferromagnetic order and spin gaps of the samples completely disappear when the doping amount x=0.2.Besides,Mn doping induces spin glass states at low temperatures,which may be due to the competition between antiferromagnetic Cr-Cr,ferromagnetic Cr-Mn and antiferromagnetic Mn-Mn.The dielectric spectrum shows that the substitution of Mn increases the dielectric constant and decreases the electrical conductivity of the sample,which satisfies the requirements for microelectronics applications due to the low dielectric loss and high dielectric constant of the material at room temperature.