The Model 372 AC resistance bridge has become the global instrument of choice for dilution refrigerator temperature monitoring and control. Did you know that the 372 is also suited to accurately and precisely perform resistivity measurements at very low temperatures?
We recently came across one such application, describing the 372 used in research performed by Brookhaven National Lab and the National High Magnetic Field Laboratory (NHMFL) at Florida State University. Their work examined superconductivity in an interesting “ultra-quantum metal” subjected to low temperature and high magnetic fields. Researchers used a 35 T resistive magnet and a He-3 cryostat at NHMFL’s DC Field Facility with Model 372 bridges to measure and derive magnetoresistivity and Hall coefficients at various temperatures.
Why was the 372 so valuable for this experiment?
- It minimized DUT self-heating (for operation down to 0.35 K) using the patented balanced current source, rejecting external sources of noise. Just imagine the difficulty making precision measurements around a 35 T magnet! Excitation levels used were as low as 31.6 µA, resulting in low dissipation powers below 10 nW while still delivering resolutions well below 1 mΩ.
- It offered a customizable excitation frequency, allowing multiple devices to be measured simultaneously, reducing the experiment runtime. This would have been extremely valuable given the range of both temperatures and field sweeps that were conducted.