Nanomagnetic devices for applications such as quantum computing and high-capacity memory cannot be developed without faster, more sensitive characterization tools to directly probe phenomena and material structures at the nanoscale. The objective of the proposed work is to advance the capability of a non-invasive, high-sensitivity technique-scanning superconducting quantum interference device (SQUID) susceptometry for the dynamic characterization of nanomagnetic systems and phenomena.
The principal investigator will achieve this objective through two innovations. First, spin sensitivity will be improved from the current state of the art, a few thousand electron spins per Hz1/2, to a few tens of spins per Hz1/2. This improvement will be accomplished by reduction of pickup loop dimensions in a combined optical and electron-beam lithography process and by utilizing an ultra-low-noise dc SQUID process. Second, bandwidth will be increased from the current state of the art, tens of kHz, to tens of MHz by the use of dc SQUID series array amplifiers as preamplifiers for the dc SQUID susceptometer.
The devices will be characterized for flux sensitivity and bandwidth at 4 K and 20 mK. The devices will have many applications at 4 K, although operation at 20 mK will be essential for the study of quantum decoherence mechanisms in electronic systems. Undergraduates, working with graduate students in the collaborator's laboratory, will characterize the spin sensitivity of the devices and their performance under realistic scanning conditions by imaging individual cobalt nanomagnetic spheres of controlled diameters ranging from 3 nm to 10 nm and magnetic moments ranging from tens to tens of thousands of electron spins. Further, one SQUID susceptometer will be used to image a second, identical device to quantitatively characterize the noise generated by the devices.
The scientific emphasis of this project is to produce sensors that will have applications in the area of nanoscale structures, novel phenomena, and quantum control and to use these sensors image both static and dynamic properties of individual cobalt nanomagnets. Integration of a high-sensitivity, high-bandwidth SQUID susceptometer into a scanning platform will significantly increase the number and kind of systems that can be studied, decrease turn-around time, and increase the number of samples that can be studied in an single experiment. Thus, the successful realization of this project will contribute to advances in nanoscale devices and system architecture. An added benefit of this project will be the educational benefits at both CU-Denver (PI's institution) and Stanford University (collaborator's institution) resulting from the collaboration between CU-Denver undergraduate students and Stanford graduate students.