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.

该个人研究者奖支持实验研究，以探索磁相变附近的空间和时间相关性，这些相变通过成分变化，压力或磁场调节到零温度。 将使用中子散射与基于实验室的热容、磁化和电输运研究的组合。 以前的工作集中在材料的相互作用的本地矩和巡回矩磁性被认为是导致形成的零温相变。该项目将探索两个系统的量子临界行为，其中磁性主要是巡回的：T=0量子反铁磁体Cr0.966V0.0034和铁磁体Zr0.95Nb0.05Zn2。 该提案的第二个主题是从基于Ce和Yb的等原子金属间化合物系列中合成新颖的近藤晶格铁磁体，特别是可以通过压力或磁场调谐的铁磁量子临界点的产生。将评估铁磁有序的稳定性和随着交换相互作用和载流子密度的修改而进行的力矩补偿过程。 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准备，成为这些设施的未来有效用户。此外，他们将接受单晶合成技术的培训，这是一个日益稀缺但有价值的研究专业。我们的主要兴趣是了解磁性可以通过修改磁性材料的组成和结构来稳定或抑制的方式，这是合理设计新型磁性材料的核心问题。所有的磁体在足够高的温度下最终都会失去它们的磁性，经历从低温状态到高温状态的相变，在低温状态下，组成原子的磁矩是对齐的和静态的，在高温状态下，磁矩波动并指向随机方向。 通过类比更熟悉的相变，如冰融化成水，我们对这些时刻开始与降低的温度对齐或排序的方式有了很多了解，首先是在短时间内的短尺度上，但最终是在整个样品上，并在任意长的时间内。该项目涉及最极端的磁体：那些在零温度极限下变得具有磁性的磁体。 与在较高温度下变成磁性的材料不同，磁矩在零温度附近但高于零温度的波动是由于它们的量子力学性质。 该项目旨在描述这种量子磁相变。它将使用各种实验技术结合中子散射与磁，热和电输运测量。 这些量子磁体的新家族的合成是这项工作的核心，而高压和高磁场将用于将磁性转变调整到零温度。 该项目广泛使用了国家研究设施，包括国家强磁场实验室和NIST、橡树岭和阿贡国家实验室的中子散射中心。 在该项目下培训的学生和博士后将成为这些设施的未来专家用户，并熟悉新型体相关电子系统的合成，这是一种罕见但非常有价值的实验技能。