Acquisition of SQUID Magnetometer - Susceptometer with Resistivity and Hall Effect Measurement Option

具有交流磁化率、电阻率和霍尔效应测量能力的SQUID磁力计将用于研究层状硫化物合金的电输运和磁性能。该研究项目将研究我们最近在BaCo1-xNixS2-y体系中发现的不寻常的金属-绝缘体转变。随着温度的降低，这种一阶相变是从半导体相转变为金属相。低温相是高度相关的金属，而高温相则表现为二维反铁磁体。转变温度和迟滞取决于化学成分。热双稳定性和与转变相关的正电阻率温度系数表明这些材料在材料研究和工程中的许多实际应用中是有用的。过渡时的大电阻变化，通过改变组成来控制性能的能力，以及材料的稳定性都有利于应用。实验计划还包括探索性合成和表征相关的三元硫化物和硒化物合金，这些合金可能表现出类似的现象或可能的超导性。所要求的设备将用于测量所发现的所有相的直流磁化率、交流磁化率、电阻率和霍尔系数。在某些层状三元硫化物中存在这种不寻常的相变是对以前未知现象的重大发现。对这些材料的研究有助于我们理解高度相关的电子系统，金属绝缘体转变，也许还有高温超导性。＊＊＊

9318333 Schweitzer The SQUID magnetometer with AC susceptibility, resistivity, and Hall effect measurement capabilities will be used to study the electrical transport and magnetic properties of layered sulfide alloys. The research project will investigate the unusual metal- insulator transition thansition that we have recently discovered in the BaCo1-xNixS2-y system. This first-order phase transition is from a semiconducting to a metallic phase with decreasing temperature. The low temperature phase is a highly correlated metal, while the high temperature phase appears to be a two- dimensional antiferromagnet. The transition temperature and hysteresis depend on the chemical composition. The thermal bistability and positive temperature coefficient of resistivity associated with the transition suggest that these materials could be useful for many practical applications in materials research and engineering. The large resistance change at the transition, the ability to control the properties by varying the composition, and the stability of the materials are all favorable for applications. %%% The experimental program will also involve exploratory synthesis and characterization of related ternary sulfide and selenide alloys that might exhibit similar phenomena or possibly superconductivity. The equipment requested will be used to measure the DC magnetization, AC magnetic susceptibility, resistivity, and Hall coefficient of all phases found. The existence of this unusual phase transition in certain layered ternary sulfides is a significant discovery of previously unknown phenomena. Study of these materials can contribute to our understanding of highly correlated electronic systems, metal- insulator transitions, and perhaps high temperature superconductivity. ***