A 3-axis Hall sensor device operating at liquid nitrogen temperature

This communication reports the design and the realization of a sensor able to measure the three components of the magnetic flux density B at 77 K above the mT range. While measuring B in these conditions is fundamental in several applications involving high-temperature superconductors, finding magnetometers operating in this range is nowadays almost impossible.
The sensor uses a commercial, room-temperature 3-axis Hall probe located in a thin cylindrical enclosure whose inner temperature is carefully controlled to be 25°C, while the outer temperature is 77 K. In order to use the sensor close to the magnetic structures to be characterized while ensuring the safety of the equipment, the active area of the Hall probe is placed at 2.2 ± 0.25 mm from the bottom of the enclosure.
The linear range of the sensor is shown to be ±217.5 mT for the axial direction and ±159 mT for the transverse directions. No temperature dependence can be observed for the offset or the sensitivity and the measurement uncertainty is typically around a few hundred µT.
Finally, we demonstrate the successful operation of this 3-axis cryogenic Hall sensor by measuring the spatial distribution of B generated by (i) a magnetized HTS axisymmetric tube, giving evidence that a flux density down to ~0.16 mT can be mapped with this sensor and (ii) an eye-shaped HTS magnet for which we measured ~10.5 mm above the centre of the structure that B is deflected by ~4° with respect to the normal to the plane of the slit.