A Prototype Three-Axis, Continuously Heating Superconducting Magnetometer

High-sensitivity Superconducting Quantum Inference Devices (SQUIDs) and mu-metal shielding have made huge advances in solving paleomagnetic noise problems. They have increased the fidelity of magnetic field variation surveys by allowing successful measurements of very weak (< 10 pAm²) magnetizations. SQUIDs have historically been expensive to buy and operate, but technological advances now allow high temperature (77 K) operation, drastically reducing their costs. Step-wise thermal paleomagnetic studies have large lag times from cycling to high temperatures and then to room temperature for measurements. If the cooling step is removed entirely, however, the lag time drops considerably. Available magnetometers currently provide either SQUID-level (0.1 - 1 pAm² sensitivity or continuous heating. Combining a SQUID magnetometer with a high temperature oven is the logical next step. However, the few that currently offer high temperature capabilities with sufficiently low noise levels require either spinning or vibrating the sample, necessitating additional handling and potentially causing damage to the sample.

Two primary factors have plagued previous developments: noise levels and temperature gradients. The superconducting components are shielded from the background magnetic field using 2 layers of mu-metal with an air gap. We use a high-powered halogen light bulb, inside of a highly reflective Inconel tube, to heat the specimen (10-20 mm diameter) slowly using infrared radiation. The Inconel tube sits inside a thin walled stainless-steel vacuum Dewar, which is poorly coupled to the 3D-printed nylon SQUID holder to minimize heat transfer. The magnetometer is designed to run Wilson method experiments, with one continuous heating and then one continuous cooling step. We report here on our latest attempts to improve the flexibility and efficiency of paleomagnetic studies.