Construction of a Low-Temperature Scanning SQUID Susceptometer

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9802719 Moler This award provides partial support for the construction of a low-temperature scanning system, designed for using miniature susceptometers to study the magnetization of individual electronic and magnetic nanostructures. The susceptometers are based on Superconducting QUantum Interference Devices (SQUIDs). Miniature SQUIDs with micron-scale spatial resolution can detect magnetic moments as small as a thousand electron spins, nine orders of magnitude smaller than can be detected by commercially available bulk magnetometers. Such sensitive magnetic measurements hold great promise for the study of qunatum chaos, macroscopic quantum coherence, superconductivity, and magnetism. At present, however, the promise of this technique is limited by the slow process of integrating each sample with its own SQUID. A scanning susceptometer would have several advantages. First, many samples could be studied in each cooldown, by placing well-separated individual mesoscopic, objects on the same substrate. Secondly, background discrimination could be much easier, since the SQUID could be moved away from the sample. Thirdly, a scanning susceptometer would not be limited to samples which can be integrated onto the same chip as the SQUID. In addtion to being an ideal tool to study mesoscopic magnetization, this apparatus could be used to make precise, quantitative, local magnetic susceptibility measurements of a wide range of materials. %%% This award will provide unique capability to study mesoscopic materials systems; is important for magnetism studies. Potential for broad impact on field. Will increase diversity in field and offer new educational opportunities.*** .