稀土钛氧化物的自旋冰和自旋液体基态、磁转变及热输运性质

Rare-earth titanates R2Ti2O7 with pyrochlore structure are a typical class of spin frustrated materials, which exhibit various magnetic states such as long-range order, spin ice, and spin liquid. This project plans to study the exotic ground states, magnetic transitions and magnetic excitations of those spin-ice or spin-liquid materials R2Ti2O7 (R = Dy, Ho, Tb, Yb). The main research contents include: (i) studying the nature of ground states and phase diagram of temperature vs magnetic field by using magnetization and specific heat measurements at very low temperatures; (ii) studying the heat transport by magnetic excitations (particularly the magnetic monopoles) or the interactions between magnetic excitations and phonons by using the thermal conductivity measurements at very low temperatures and under high magnetic fields; (iii) studying the ground states and magnetic field induced transitions by using the heat transport experiments; (iv) growing single crystals with rare-earth or non-magnetic Y doping to modify the crystal structures and magnetic interactions, for the purpose of studying the crossover between different magnetic states. Based on these experimental works, we try to reveal the mechanisms how the spin exchange, spin anisotropy, spin dipole interactions, and spin frustration determine the magnetic and heat-transport properties of R2Ti2O7 materials.

具有烧绿石结构的稀土钛氧化物R2Ti2O7（R为稀土元素）是一类典型的自旋阻挫材料，展现出长程磁有序、自旋冰、自旋液体等多种不同的磁性。本项目以具有自旋冰、自旋液体等奇特磁性的一些体系（R = Dy,Ho,Tb,Yb）为研究对象，以这些材料基态磁性质、磁转变及磁激发特性为主要研究内容，拟开展以下工作：利用极低温磁学、比热等测量研究基态磁性质与温度-磁场相图；利用极低温强磁场下的热输运性质，对磁激发（特别是可能产生的磁单极子）热传导或磁激发－声子的相互作用进行深入研究，并由此研究基态磁性及外磁场引起的磁转变现象；进行稀土元素和非磁性Y元素相互掺杂的单晶材料制备，以改变这些材料的晶体结构和磁相互作用，从而研究不同磁性的相互渡越行为。通过以上实验研究，揭示磁交换作用、磁各向异性、磁偶极作用、自旋阻挫等因素对R2Ti2O7材料磁性和热输运性质的决定机制。