Magnetic Correlations and Quantum Critical Points

磁关联和量子临界点

• 批准号: 0405961
• 负责人: Meigan Aronson
• 金额: $ 33万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-06-01 至 2007-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0405961&HistoricalAwards=false
• 关键词: Magnetic; Correlations; Quantum; Critical; Points

This individual investigator award supports experimental investigations to explore the spatial and temporal correlations near magnetic phase transitions, which are tuned to zero temperature by compositional variation, pressure, or magnetic field. A combination of neutron scattering with lab-based heat capacity, magnetization, and electrical transport studies will be used. Previous work focused on materials where the interplay of local moment and itinerant moment magnetism is thought to lead to the formation of the zero temperature phase transition. This project will explore the quantum critical behaviors of two systems where the magnetism is predominantly itinerant: the T=0 quantum antiferromagnet Cr0.966V0.0034, and the ferromagnet Zr0.95Nb0.05Zn2. The second theme of the proposal is the synthesis of novel Kondo lattice ferromagnets from the Ce and Yb based equiatomic intermetallic series, especially the generation of ferromagnetic quantum critical points that can be tuned by pressure or magnetic field. The stability of ferromagnetic order and the process of moment compensation as the exchange interaction and carrier density are modified will be assessed. This project makes extensive use of national research facilities, and the students and postdocs involved in the research will be well prepared to become effective future users of these facilities. Further, they will be trained in single crystal synthesis techniques, an increasingly scarce but valuable research specialty. Our primary interest is to understand the ways in which magnetism can be stabilized or alternatively suppressed by modifications to the composition and structure of magnetic materials, an issue that is central to the rational design of new classes of magnetic materials. All magnets ultimately lose their magnetic properties at sufficiently large temperatures, undergoing a phase transition from a low temperature state where the magnetic moments of the constituent atoms are aligned and static, to a high temperature state where the moments fluctuate and point in random directions. By analogy to more familiar phase transitions, such as the melting of ice into water, much is known about the way in which these moments begin to align or order with reduced temperature, first on short length scales and for short times, but ultimately over the entire sample and for arbitrarily long times. This project addresses the most extreme magnets: those that become magnetic in the limit of zero temperature. Unlike materials that become magnetic at higher temperatures, the fluctuations of the magnetic moments near but above zero temperature are due to their quantum mechanical nature. This project seeks to characterize this sort of quantum magnetic phase transition. It will use a variety of experimental techniques combining neutron scattering with magnetic, thermal, and electrical transport measurements. Synthesis of new families of these quantum magnets is central to this effort, while high pressures and high magnetic fields will be used to tune magnetic transitions to zero temperature. This project makes extensive use of national research facilities, including the National High Magnetic Field Laboratory and the neutron scattering centers at NIST, Oak Ridge, and Argonne National Laboratories. Students and postdocs trained under this project will be expert future users for these facilities, as well as being conversant in the synthesis of novel bulk correlated electron systems, a rare but highly valued experimental skill.

该单独的研究者奖支持实验研究，以探索磁相跃迁附近的空间和时间相关性，这些空间和时间相关性通过组成变化，压力或磁场将其调整为零温度。 将使用中子散射与基于实验室的热容量，磁化和电运输研究的结合。 先前的工作集中在材料上，材料的局部矩和巡回力矩磁性的相互作用被认为会导致零温度相变的形成。该项目将探索两个系统的量子关键行为，其中磁性主要是行动的：t = 0量子抗Fiferromagnet CR0.966V0.0034和Ferromagnet ZR0.95NB0.05ZN2。 该提案的第二个主题是从CE和基于YB的等准层间套件中合成新型的Kondo Lattice Ferromagnet，尤其是可以通过压力或磁场调节的铁磁量子临界点的产生。随着交换相互作用和载体密度的修改，铁磁顺序的稳定性以及力矩补偿的过程将得到评估。 该项目广泛利用国家研究设施，参与研究的学生和博士后将做好充分的准备，以成为这些设施的有效用户。此外，它们将接受单晶合成技术的培训，这是一种越来越稀缺但有价值的研究专业。我们的主要兴趣是了解通过对磁性材料的组成和结构进行修改，可以稳定或抑制磁性的方式，这对于新的磁性材料的合理设计至关重要。所有磁铁最终在足够大的温度下失去其磁性特性，从低温状态进行相变，使组成原子的磁矩被对齐并静态，到矩矩波动并在随机方向上波动的高温状态。 与更熟悉的相变相似，例如将冰熔化到水中的融化，这些时刻开始与温度降低的方式对齐或有序，首先是在短长度和短时间内，但最终在整个样品中，并且在整个样品中最终任意长时间。该项目解决了最极端的磁铁：在零温度极限的磁性磁铁。 与在较高温度下磁性的材料不同，磁矩接近但高于零温度的波动是由于其量子机械性质引起的。 该项目旨在表征这种量子磁相变。它将使用多种将中子散射与磁性，热和电运传输测量结合的实验技术。 这些量子磁体的新家族的合成对于这项工作至关重要，而高压和高磁场将用于调整磁性转变至零温度。 该项目广泛使用了国家研究设施，包括国家高磁场实验室和NIST，Oak Ridge和Argonne National Laboratories的中子散射中心。 在该项目下培训的学生和博士后将是这些设施的未来未来用户，并且是熟悉新型散装相关电子系统的熟悉，这是一种罕见但非常有价值的实验技能。