Synthesis and Crystal Growth of Dilute Magnetic Semiconductors and Frustrated Magnets

“这项奖励是根据2009年美国复苏和再投资法案（公法111-5）资助的。”技术概述：新材料的合成和晶体生长将集中在稀磁半导体和受挫磁体上，并将这些材料制备为粉末、单晶和薄膜。粉末将产生关于固溶体形成程度的信息；扩散或离子注入过渡金属到单晶衬底将允许铁磁性的成分映射；单晶的通量生长为中子散射表征材料的合成提供了一条途径；低温下的薄膜沉积将允许研究典型的相分离成分。选择稀释磁性半导体和受挫磁体这两类要研究的材料，分别是由于对自旋电子应用和多铁性的强烈兴趣。半导体晶格将被各种第一排过渡金属磁性离子取代，包括钒、铬、锰、铁、钴和镍。过渡金属取代的浓度约为5%，因此磁性离子之间的直接相互作用可以忽略不计（稀释）。由于与半导体中的电子载流子相互作用，这些稀磁性半导体材料表现出远距离磁耦合（铁磁性）。基于载流子诱导铁磁性理论，研究了带隙能、载流子密度和交换耦合强度等因素对铁磁居里温度的影响。因此，三元磷化物、砷化物、硒化物和碲化物材料被预测为载流子介导铁磁性的强候选宿主晶格。对于磁性受挫材料，将探索以下化合物的高温单晶生长：ACr2S4，其中A= Zn， Cd或Hg，以研究依赖于最近和次近邻Cr相互作用与Cs2Cu3ZrF12之间相互作用的磁性（以及CdCr2S4的可能结构性质），以研究导致不寻常磁性现象的强几何挫折。非技术概要：稀磁半导体和受挫磁体的发现和理解可以推动微电子和光电子工业，可能导致基于自旋电子学的新器件。此外，由高中生、本科生和研究生以及博士后组成的研究小组成员将接受科学、技术、工程和数学（STEM）学科的研究培训。由于纽约城市大学（CUNY）的纽约城市学院（CCNY）的人口结构，许多女学生和来自代表性不足的族裔的学生将接受研究方面的培训。由化学系和物理系参与的多小组会议将促进内部合作；纽约市地区固体化学专题讨论会将开始交流和传播结果；和磁性材料将与美国和世界各地的其他实验室共享，以追求对磁相互作用的理解。为了进一步补充科学和教育方面的内容，当地公众将通过开放日、科学展览和当地高中团体的校园参观来了解晶体化学。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."TECHNICAL SUMMARY:The synthesis and crystal growth of novel materials will focus on dilute magnetic semiconductors and frustrated magnets with the preparation of these materials as powders, single crystals, and thin films. The powders will yield information on the extent of solid solution formation; diffusion or ion implantation of transition metals into single crystal substrates will allow for compositional mapping of ferromagnetism; flux growth of single crystals will provide a route to synthesize materials for characterization by neutron scattering; and thin film deposition at low temperatures will permit the study of compositions which typically demonstrate phase separation. The two classes of materials to be investigated, dilute magnetic semiconductors and frustrated magnets, are chosen due to the intense interest in spintronic applications and multiferroic behavior, respectively. Semiconductor crystal lattices will be substituted with various first row transition metal magnetic ions including vanadium, chromium, manganese, iron, cobalt and nickel. The transition metal substitution will have concentrations around five atomic percent such that there is negligible direct interaction between magnetic ions (dilute). These dilute magnetic semiconductor materials demonstrate long range magnetic coupling (ferromagnetism) due to interaction with electronic carriers in the semiconductor. Based on theories of carrier-induced ferromagnetism, several variables, including the bandgap energy, carrier density and exchange coupling strength, affect the ferromagnetic Curie temperature. Therefore, ternary phosphide, arsenide, selenide and telluride materials are predicted to be strong candidate host lattices for carrier-mediated ferromagnetism. For the frustrated magnetic materials, the growth of single crystals from high temperature fluxes will be explored for the following compounds: ACr2S4, where A= Zn, Cd or Hg, in order to study the magnetic properties (and possible structural properties in the case of CdCr2S4) which depend on the interplay between the nearest and next nearest neighbor Cr interactions and Cs2Cu3ZrF12 to investigate strong geometrical frustration which leads to unusual magnetic phenomena.NON-TECHNICAL SUMMARY:The discovery and understanding of dilute magnetic semiconductors and frustrated magnets can advance the microelectronics and photonics industries, possibly leading to new devices based on spintronics. In addition, the members of the research group, which consists of high school students, undergraduate and graduate students, and postdoctoral associates will receive research training in the Science, Technology, Engineering and Mathematics (STEM) disciplines. Due to the demographics at The City College of New York (CCNY) of the City University of New York (CUNY), many female students and students from underrepresented ethnic groups will be trained in research. Multi-group meetings involving the chemistry and physics departments at CCNY will promote internal collaboration; a symposium for solid state chemistry in the New York City area will initiate communication and dissemination of results; and magnetic materials will be shared with other laboratories within the United States and around the world to pursue the understanding of the magnetic interactions. To further supplement the science and educational aspects, the local public will be introduced to crystal chemistry on open house days, science fairs and campus visitations by local high school groups.