Magnetic Study Of Transition Metal Oxides A₂Co₂TeB₂O₁₀（A=Pb,Ba）and SrCo（SeO₃）₂

In recent years,low-dimensional quantum systems have attracted great interest in condensed matter physics due to their unique properties,such as quantum spin liquids,spin-induced multiferroicity,quantum magnetization platforms,and Bose-Einstein condensates.Up to now,the reported low-dimensional quantum magnetic materials are still limited,and the exploration of new low-dimensional quantum magnetic materials is important for understanding the physics of these phenomena.In this thesis,we successfully synthesized two new quasi-1D magnetic materials A₂Co₂TeB₂O₁₀（A=Pb,Ba）and SrCo（SeO₃）₂,and systematically investigated their structures,magnetic properties and specific heats.In addition,we performed theoretical calculations on Pb₂Co₂TeB₂O₁₀ and confirmed its antiferromagnetic ground state.The details are organized as follows.Chapter 1 gives a brief introduction to low-dimensional quantum systems.The chapter starts with a description of the exotic physical properties exhibited by low-dimensional quantum magnetic materials,which is followed by an overview of some classical low-dimensional quantum magnetic materials.In Chapter 2,the experimental method and the instruments required for the physical characterization used in this thesis are described.The experimental method is the high temperature solid phase method,which contains weighing,grinding,pre-sintering,pressing,and sintering.The instruments required for testing include X-ray powder diffractometer（XRD）and physical property measurement system（PPMS）.The composition of the sample is tested by XRD for structural characterization,and the magnetic properties and specific heat of the sample are tested by PPMS for physical characterization.Chapter 3 systematically investigates the synthesis,structure and magnetization of A₂Co₂TeB₂O₁₀（A=Pb,Ba）compounds.The results show that the space group of A₂Co₂TeB₂O₁₀（A=Pb,Ba）is Cmca.And the magnetization results indicate that A₂Co₂TeB₂O₁₀（A=Pb,Ba）undergoes an antiferromagnetic（AFM）phase transition at～45 K for Pb₂Co₂TeB₂O₁₀ and at～30 K for Ba₂Co₂TeB₂O_10.The fitted Curie-Weiss temperatures areθcw=-29.4 K for Pb₂Co₂TeB₂O₁₀ andθcw=-18.03 K for Ba₂Co₂TeB₂O₁₀,indicating the relatively strong AFM interactions.In Chapter 4,the physical properties of SrCo（SeO₃）₂ are systematically investigated.The space group of SrCo（SeO₃）₂ is P2₁/c.And SrCo（SeO₃）₂ undergoes an AFM phase transition at T_N～22 K,which is significantly influenced by magnetic field.The Curie-Weiss fitting yields a Curie-Weiss temperatureθ_cw=-32.8 K,implying a dominant AFM interaction.The effective magnetic moment isμ_eff=4.6μ_B,which is much higher than the theoretical value,indicating the existence of remnant orbital moments.Chapter 5 shows the summary of this thesis and the outlook of future research.