| In frustrated spin-chain materials, a variety of quantum states will be formed because of frustration and the quantum fluctuation. External parameters, such as the magnetic field, the temperature and the carrier concentration will greatly influence the nature of the magnetic ground states and excited states, leading to a rich and complex magnetic phase diagram and the quaint quantum critical phenomena, such as multiferroicity, nematic phase, spin liquid state. In recent years, the studies of the heat transport not only reflect the material’s heat-transport capability, but also indicate the characteristics and properties of the elementary excitations, including phonon, magnon, which has an important significance on microscopic physical properties research of the frustrated spin-chain materials. In this thesis, the text is divided into two chapters, and the main content of each chapter is as follows:In the first chapter, we show the basic properties of low-dimensional quantum magnets, including the theoretical and experimental results of typical low-dimensional systems:the S=1/2 spin chain, S=1 Haldane chain,S=1/2 spin ladder,S=1/2 spin Peierls materials.S=1/2 J1-J2 frustrated spin chain has been a hotspot of current research, of which frustration and quantum fluctuation bring out the rich ground state phase diagram and many exotic phenomena. PbCu(SO4)(OH)2 and LiCuVO4 displayed the multiferroic behavior caused by the quantum effect, while the quantum spin liquid state was referred in LiCuSbO4 for no spin order appeared until 100 mK. We introduce the crystal structure, magnetic structure, thermodynamic properties and the characteristics of the magnetic excitation of Ca2Y2Cu5O10, which is near the critical point of S=1/2 J1-J2 frustrated spin chain and known to have the double branch in magnetic excitation spectrum. Then, we discuss the importance of thermal conductivity in low-dimensional magnetic materials, including phonon thermal conductivity, magnon thermal conductivity, among which the determination and characteristic of the magnon thermal conductivity are discussed.In the second chapter, we study the crystal growth of Ca2Y2Cu5O10 and find that the growth speed, atmosphere, flux are the important factors that affect the quality of single crystal. The magnetic properties and the zero-field heat capacity are measured. It is found that:(ⅰ)the spins of Ca2Y2Cu5O10 are along the direction of b, i.e., the b axis is spin-easy axis; (ⅱ) the antiferromagnetic transition occurs at 29.5 K. By using the Debye model and Einstein model, the phonon contribution to heat capacity of 1.8 K to 300 K is fitted successfully. By deducting the phonon contribution, the magnetic specific heat and magnetic entropy are obtained. Then the thermal conductivities along the direction of a and b axes of Ca2Y2CusO10 single crystal were carried and showed a phonon peak in～20 K and a kink character at the antiferromagnetic transition. After fitting thermal conductivity by using the Debye model considering the critical fluctuations, we find that the thermal conductivity perpendicular to the spin chain is mainly due to the phonon contribution while the thermal conductivity along the chain direction can be fitted only at low temperatures. It seems that the high-temperature deviation is due to the magnetic heat transport. Through substracting the fitted curve from measured curve, we get the thermal conduction and the thermal Drude weight of the magnetic excitations. |
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