NSF-Europe: Collaborative Study of Geometrically Frustrated Magnetic Material: New Materials and New Physics

这是一个国际合作研究项目，是应NSF征集NSF 02-135的要求提交的。该项目将研究几何受挫磁体的不同寻常的性质，这种材料中原子自旋之间的相互作用由于磁性亚晶格的三角形几何而相互竞争。这导致了高度简并的基态，其中相互作用能量不能同时最小化。这反过来又防止了普通的磁有序降到远低于自旋-自旋相互作用的能量标度的温度。低温磁性研究将由两名专门从事材料化学和磁热动力学测量的美国研究人员和两个欧洲小组合作进行，其中一个小组在巴黎-南德大学物理固体实验室的核磁共振(NMR)和其他测量领域，另一个小组在伦敦大学学院的中子衍射和理论领域。其中一个研究主题是新的几何受挫磁体的化学合成，其具体目标是研究新的受挫晶格类型，并寻找既高度受挫又可以作为高质量单晶样品生长的材料。第二个主题是研究化学取代对几何受挫体系的影响。参与研究的学生将参与国际研究活动，以及传统和前沿的培训，为他们在学术界、行业或政府的职业生涯做好准备。%这是一个国际合作研究项目，是应NSF征集NSF 02-135的要求提交的。该项目将研究一种被称为几何受挫磁铁的材料的不同寻常的特性。与普通磁体相比，由于晶格中磁原子的几何排列，这些材料无法获得独特的、低温、最低能量的磁矩排列。导致这种效果的关键几何图形是将磁性原子放置在三角形的顶点上。这些体系与其他磁性材料的根本不同之处在于，它们在低温下的性质不能用目前的理论模型来理解。了解磁体中的几何受挫对超导结阵列或神经网络等各种复杂系统都有意义，也可能为计算算法提供洞察。这项研究是由四个小组合作完成的，其中两个在美国，一个在英国，一个在法国。这两名美国调查人员长期以来一直与不同的学生群体合作，并让研究生和本科生参与研究过程的每个阶段。参与研究的学生将参加国际研究活动，以及传统和尖端培训，为他们在学术界、行业或政府的职业生涯做好准备。

This is an international collaborative research project that was submitted in response to NSF Solicitation NSF 02-135. The project will investigate the unusual properties of geometrically frustrated magnets, materials in which the interactions between atomic spins compete with each other due to the triangular geometry of the magnetic sublattice. This leads to highly degenerate ground states where the interaction energies cannot all be simultaneously minimized. This in turn prevents ordinary magnetic ordering down to temperatures well below the energy scale of the spin-spin interaction. The low temperature magnetic properties will be investigated via a collaborative approach involving two U.S. investigators, who specialize in materials chemistry and magnetothermodynamic measurements, and two European groups: One in the areas of nuclear magnetic resonance (NMR) and other measurements at Laboratoire de Physique des Solides, Universite Paris-Sud, the other in the areas of neutron diffraction and theory at University College London. One research theme is the chemical synthysis of new geometrically frustrated magnets with the specific goals of investigating new frustrating lattice types and of finding materials that are both highly frustrated and that can be grown as high-quality single crystal samples. The second theme is the study of effects of chemical substitution on geometrically frustrated systems. Students involved in the research will participate in international research activities, together with traditional and cutting edge training that will prepare them for careers in academe, industry or government.%%%This is an international collaborative research project that was submitted in response to NSF Solicitation NSF 02-135. The project will investigate the unusual properties of a class of materials known as geometrically frustrated magnets. In contrast to ordinary magnets, and due to the geometrical arrangement of magnetic atoms in the lattice, these materials cannot attain a unique, low temperature, lowest-energy arrangement for their magnetic moments. The key geometry leading to the effect has magnetic atoms placed at the vertices of triangles. These systems are fundamentally different from other magnetic materials in that their properties at low temperatures cannot be understood within current theoretical models. Understanding geometrical frustration in magnets has implications for complex systems as diverse as superconducting junction arrays or neural networks, and may also provide insight into computational algorithms. The research is a collaboration between four groups, two in the U. S., one in the United Kingdom and one in France. The two U.S. investigators have a long record of working with a diverse group of students and involving graduate students and undergraduates in every stage of the research process. Students involved in the research will participate in international research activities, together with traditional and cutting edge training that will prepare them for careers in academe, industry or government.