α-Li2IrO3和Na2BaCo(PO4)2等阻挫磁体的材料拓展和物性研究

迫使量子磁矩位于蜂窝或三角形晶格中，可以增强磁矩之间的一些量子力学 相互作用，产生常规磁性系统中难以出现的奇异磁阻挫或临界行为。目前，人们 已经发现了一些可能实现这些奇异行为的物质，比如 𝛼-Li2IrO3 和 Na2BaCo(PO4)2 等，但对其机理尚未充分理解。在此基础上，我们开展了进一步的材料拓展和物 性研究。通过测量拉曼光谱、𝜇 子自旋弛豫、磁矩、和热容，我们对六种绝缘晶体 磁体进行了磁性的分析，其中四种是新化合物。研究结果主要有：（1）𝛼-Li2IrO3 和 H3LiIr2O6 在高能区域具有鼓包形状的磁拉曼连续谱，表明其可能存在分数化 磁激发；H3LiIr2O6 的 𝜇 子自旋弛豫数据在低能区域具有 𝐴(𝐵, 𝑡) ≈ 𝐴(𝑡/𝐵0.5) 的标 度行为，表明其磁激发的态密度可能具有形式：𝑁(𝐸) ∝ 𝐸−0.5。（2）四种新化合物Na2SrCo(PO4)2、Na2SrNi(PO4)2、Na2SrNi(VO4)2、Li2BaCo(PO4)2 分别是 𝑗 = 1/2 等腰三角形晶格反铁磁体（低温）、𝑗 = 1 等腰三角形晶格反铁磁体、𝑗 = 1 等腰 三角形晶格易面铁磁体、𝑗 = 1/2 等边三角形晶格易面铁磁体（低温）。（3）当 磁场垂直于 Na2SrCo(PO4)2 的三角形晶格时，其磁场-温度相图上可能存在一系列 新磁相，在饱和磁场附近，它还表现出可能的二维临界行为。（4）当磁场垂直于 Na2SrNi(VO4)2 的三角形晶格时，其在饱和磁场附近表现出可能的二维到三维临界 行为。这些结果将有助于发展物质磁阻挫和临界行为的量子力学模型，加深人们 对物质磁性的理解，甚至应用于下一代功能材料和器件。

Forcing quantum magnetic moments to lie in honeycomb or triangular lattice strengthens some of the quantum mechanical interactions between the moments. In this way, it is possible to produce exotic magnetic frustration or critical behaviors not seen in conventional magnetic systems. Although some substances that may realize these exotic behaviors have been discovered, such as 𝛼-Li2IrO3 and Na2BaCo(PO4)2, etc., the mechanism has not been fully understood. On this basis, we carried out further material expansion and physical properties research. By measuring Raman spectroscopy, muon spin relaxation, magnetic moment, and heat capacity, we have analyzed the magnetic properties of six insulating crystalline magnets, four of which are new compounds. The results show that: (1) 𝛼-Li2IrO3 and H3LiIr2O6 have bulge-shaped magnetic Raman continuum in the high-energy region, indicating possible fractional magnetic excitation; for H3LiIr2O6, the observation of scaling behavior of muon spin relaxation data 𝐴(𝐵, 𝑡) ≈ 𝐴(𝑡/𝐵0.5) in the low-energy region indicates the magnetic excitation may have the form: 𝑁(𝐸) ∝ 𝐸−0.5. (2) Four new compounds Na2SrCo(PO4)2, Na2SrNi(PO4)2, Na2SrNi(VO4)2, Li2BaCo(PO4)2 are isosceles triangular lattice antiferromagnet with 𝑗 = 1/2 (low temperature), isosceles triangular lattice antiferromagnet with 𝑗 = 1, isosceles triangular lattice easy-plane ferromagnet with 𝑗 = 1, equilateral triangular lattice easyplane ferromagnet with 𝑗 = 1/2 (low temperature), respectively. (3) When the magnetic field is perpendicular to the triangular lattice of Na2SrCo(PO4)2, a series of new magnetic phases may exist on its magnetic field-temperature phase diagram, and it exhibits possible two-dimensional critical behavior near the saturated magnetic field. (4) When the magnetic field is perpendicular to the triangular lattice of Na2SrNi(VO4)2, it exhibits possible two- to three-dimensional critical behavior near the saturated magnetic field. These findings will contribute to the development of quantum mechanical models of magnetic frustration and critical behavior of matter, deepen our understanding of matter magnetism, and even be applied to next-generation functional materials and devices.

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