Miniature Thin-Film SQUID Susceptometer for
Magnetic Microcalorimetry and Thermometry

S. T. P. Boyd, Vincent Kotsubo, Robin Cantor, Alexander Theodorou, and J. Ad Hall

Abstract— We have developed a miniature thin-film SQUID susceptometer for research in magnetic microcalorimetry and miniature magnetic thermometry. We have previously reported measurements at 4K characterizing performance of the first generation of this device using modulation-based flux-locked feedback electronics and at ~50mK using a spherical superconducting test sample. Here we describe design, fabrication, and new measurements of the second generation of the device using two-stage SQUID amplification to characterize the improved noise, bandwidth, persistence switch and field coil performance. The device now meets or exceeds all requirements for magnetic microcalorimetry sensor testing, achieving noise of ~0.75μΦ₀/√Hz and bandwidth ~1.2MHz near 50mK, and trapping and stably holding magnetizing field of at least 5.9mT.

Index Terms— Detectors, SQUID magnetometers, Superconducting switches

Manuscript received 19 August 2008. This work was supported by the U.S. Defense Threat Reduction Agency.
S. Boyd, V. Kotsubo, and A. Theodorou, are with the Department of Physics and Astronomy, University of New Mexico, MSC07-4220, Albuquerque, NM 87131-0001 USA (corresponding author: S. Boyd, phone: 505-277-4439; fax: 505-277-1520; e-mail: stpboyd@unm.edu; V. Kotsubo email: vkotsubo@earthlink.net; A. Theodorou email: alext@unm.edu).
R. Cantor and J. Hall are with STAR Cryoelectronics, Santa Fe, NM, 87508 USA. (R. Cantor email: rcantor@starcryo.com; J. Hall email: ahall@starcryo.com).

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