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Hall sensor-based magnetometry based on miniaturized 2DEG Hall sensors is developed at the LSI since the advent of the cuprate HTSC. Development of such metrology-oriented devices has been supported by ANR “Micromag” (2008-2011), in partnership with the RD team of ITRON, a company producing electric counters based on such sensors. The design and fabrication of a new generation of sensors by ion implantation technology was the main achievement of this project. Apart from the two most widely used designs of the following figure, other designs include sensors for scanning devices and sensors with incorporated switches for spinning current noise reduction.

Two Hall sensor designs. Left: AC susceptometer with reduced pick-up coil. Right: gradiometer composed of a line of 10 5 × 5 µm2 sensors, spaced by 20μm.

The sensors have allowed multiple collaborations, such as the study of magnetic noise in the ferro-fluids (collaboration with CEA / IRAMIS / SPEC). Ferro-fluid, formed by the suspension of magnetic nanoparticles in glycerol, mimic a spin-glass system with reduced number of particles. It undergoes magnetic phase transition analogue of spin glass and it is a model system showing breakdown of dissipation-fluctuation relation in non-ergodic systems. Post-doctorate visitor Katsuyoshi Komatsu realized measurements of low frequency magnetic noise.