Order from Disorder: Tuning Long-Range Magnetic Ordering by Chemical Doping in Strongly Correlated Intermetallics

* 技术摘要 * 提出了一种新的金属间化合物系统中的电子和磁基态的实验研究。 重点将集中在小带隙半导体的合成和表征，包括一系列与FeGa 3和碱土金属和稀土金属六硼化物有关的化合物。这些强相关电子材料的性质敏感地依赖于诸如样品化学计量、载流子密度、温度、化学/物理压力和磁场等参数。 本文研究了非磁性半导体FeGa_3中化学掺杂引起的长程磁有序。 铁磁量子临界点（FM-QCP）是最近发现的，它指向一种新的驱动临界性的结构特征-混合价Fe-Fe二聚体“单线态”密度。 其次，本计画将探讨提高掺杂近藤绝缘体铁磁有序化温度的可能性。 FeSi是典型的例子，并且显示出与FeGa 3类似的性质。 反常霍尔效应的测量已被证明是预测材料的自旋电子学应用潜力的一个很好的参数。 最后，提出了高质量单晶六硼化物材料的辐照研究，以验证高Tc弱铁磁性的机制。 在这种情况下，系统中的无序源于硼亚晶格中的空位。 这项实验研究将为博士后，研究生和本科生提供材料合成，结构表征，物理特性测量作为温度和磁场的函数以及数据采集和分析等领域的宝贵经验和培训。 * 非技术摘要 * 这项拟议的研究将集中在具有非常独特的物理性质的材料的合成。 例如，半导体和磁性材料是当今许多先进技术和设备的核心。这个项目将研究如何故意无序材料，无论是化学，或与缺陷，可以导致增强的物理性能，如高温磁性。 这项拟议的研究计划将有助于理解一般的强相关电子系统，并可能导致新材料的应用，例如在新兴的自旋电子学（基于自旋的电子学）领域，这可能会彻底改变计算机存储器行业。 博士后，研究生和本科生将获得材料合成，结构表征，物理性能测量以及数据采集和分析领域的宝贵经验。 该研究项目的一个主要组成部分是材料合成，它为教学和研究之间提供了一个天然的桥梁，特别是对本科生。 他们能够在相对较短的时间内利用各种固态物理和化学技术做出真实的贡献。 此外，新材料的合成对美国在先进技术竞赛中保持竞争力至关重要。

****Technical Abstract****An experimental investigation of the electronic and magnetic ground states in novel intermetallic systems is proposed. Emphasis will focus on the synthesis and characterization of small band-gap semiconductors, including, a series of compounds related to FeGa3 and the alkaline earth and rare earth hexaborides. The properties of these strongly correlated electron materials depend sensitively on parameters such as sample stoichiometry, carrier density, temperature, chemical/physical pressure, and magnetic field. The long-range magnetic order induced by chemical doping in the non-magnetic semiconductor FeGa3 will be studied. A ferromagnetic quantum critical point (FM-QCP) was recently discovered which points toward a novel structural feature driving the criticality - the density of mixed valent Fe-Fe dimer "singlets". Second, this project will investigate the possibility of raising the ferromagnetic ordering temperature in doped Kondo insulators. FeSi is the classic example, and shows similar properties to that of FeGa3. Measurements of the anomalous Hall effect have shown to be an excellent parameter in predicting a material's potential for spintronics applications. Finally, an irradiation study of high quality single crystals of hexaboride materials is proposed in an effort to verify the mechanism of the high-Tc weak ferromagnetism. In this case, the disorder in the system stems from vacancies in the boron sublattice. This experimental research will provide post-doctoral associates, graduate, and undergraduate students with valuable experience and training in the areas of materials synthesis, structural characterization, measurement of physical properties as a function of temperature and magnetic field, and data acquisition and analysis. ****Non-Technical Abstract****This proposed research will focus on the synthesis of materials that possess very unique physical properties. Semiconductors and magnetic materials, for example, are at the heart of many of today's advanced technologies and devices. This project will investigate how intentionally disordering a material, either chemically, or with defects, can result in enhanced physical properties, such as high temperature magnetism. This proposed research program will aid in the understanding of strongly correlated electron systems in general, and may result in new materials for applications, such as in the emerging field of spintronics (spin-based electronics), which could revolutionize the computer memory industry. Post-doctoral associates, graduate, and undergraduate students will gain valuable experience in the areas of materials synthesis, structural characterization, measurement of physical properties, and data acquisition and analysis. A major component of this research project is in materials synthesis, which provides a natural bridge between teaching and research, especially for undergraduates. They are able to make real contributions in a relatively short amount of time, utilizing a variety of solid state physics and chemistry techniques. Furthermore, the synthesis of new materials is vital to the United States remaining competitive in the race for advanced technologies.