稀土钙钛矿YbM(M=Al, Cr)O3体系的一维量子磁性研究

ONE-DIMENSIONAL QUANTUM MAGNETISM OF RARE EARTH PEROVSKITE YbM(M=Al, Cr)O3

葛晗

11849419

硕士

物理学

吴留锁

2020-05-28

2020-07-06

哈尔滨工业大学

深圳

钙钛矿材料ABO3一直以来都是人们关注的焦点。由于其结构变形体和B位金属离子的多样性，还有电子、自旋、轨道、电荷和晶格自由度之间各种微观的相互作用和微妙的平衡，使得我们能够观察到多种奇特的物理现象。而稀土钙钛矿更是因为4f和3d晶格之间的耦合作用产生了许多有趣的磁学现象，例如多铁性、自旋重取向、量子临界现象等。因此，本文系统地研究了稀土钙钛矿YbM(M=Al, Cr)O3体系，探索了其中的磁学性质以及量子临界现象等。YbAlO3是一种一维量子磁体，其强烈的量子涨落引起了许多新奇的现象。通过对YbAlO3进行磁热效应的研究，更加清晰地认识了YbAlO3在低温下的相图，并且观察到了量子临界点附近的非公度反铁磁相中出现的1/3及1/2的量子化平台。这些量子化平台的发现对今后理论的发展以及低维量子磁体中量子临界现象的解释都具有重要的意义。而通过将非磁性的Al3+换为有磁性的Cr3+，我们系统地研究了YbCrO3这一材料的晶体生长以及低温磁性等。通过助熔剂法生长出了高质量的单晶样品。借助于中子散射技术，确定了YbCrO3的磁结构为FxCyGz型，Yb3+与Cr3+之间以反铁磁的形式耦合在一起。然而，Yb3+位置的磁矩很小，这表明大多数Yb矩没有完全极化。通过对YbCrO3的磁化率以及比热测量，我们还系统研究了它的磁学性质及热力学性质。在低温下观察到负磁化现象，这与预期的Yb3+与Cr3+之间反铁磁耦合是一致的。

The perovskite material with the chemical composition ABO3 has attracted great attention. Due to the diversity of its structural deformation and M-site metal ions, as well as various microscopic interactions and delicate balances between electrons, spins, orbits, charges and lattice freedom, we can observe a variety of novel physical phenomenon. The rare earth perovskite has many interesting magnetic phenomena, such as multiferroicity, spin reorientation, and quantum critical phenomena, because of the coupling between the 4f and 3d sublattices. Therefore, this dissertation systematically studied the rare earth perovskite YbM(Al, Cr)O3 system, and explored their magnetic properties as well as quantum critical phenomena.YbAlO3 is a one-dimensional quantum magnet, and its strong quantum fluctuations have caused many novel phenomena. By exploring the magnetocaloric effect of YbAlO3, the phase diagram of YbAlO3 at low temperature was depicted more clearly. In addition, the 1/3 and 1/2 quantized plateaus in the IC-antiferromagnetic phase near the quantum critical point was observed. The discovery of these quantized platforms has a very important significance for future theoretical development and the interpretation of quantum critical phenomena in low-dimensional quantum magnets.By replacing nonmagnetic Al3+ with magnetic Cr3+, we studied the crystal growth and low-temperature magnetism of YbCrO3. A high-quality single crystal sample was grown by the flux method. Neutron scattering experiments were performed, and the magnetic structure of YbCrO3 is determined to be FxCyGz-type. The powder neutron diffraction measurements inditate that Yb3+ and Cr3+ are antiferromagnetically coupledas previously reported. However, the refined ordered moment of Yb site is very small, suggesting that most of the Yb moments are not fully polariezed. The magnetization and specific heat of YbCrO3 were systematically studied as well. Negative magnetization was observed at low temperatures, which is consistent with the expectation that Yb and Cr sites are antiferromagnetically coupled.

一维量子磁体 磁热效应 量子临界现象 磁结构 自旋翻转

one-dimensional quantum magnet magnetocaloric effect quantum critical phenomenon magnetic structure spin flip

中文

联合培养

南方科技大学

葛晗. 稀土钙钛矿YbM(M=Al, Cr)O3体系的一维量子磁性研究[D]. 深圳. 哈尔滨工业大学,2020.