Multilayer MgB2 superconducting quantum interference filter magnetometers

We report two types of all-MgB2 superconductive quantum interference filter (SQIF) magnetometers that can measure absolute magnetic fields with high sensitivity. In one configuration, the SQIFs were made of 20 multilayer nonplanar all-MgB2 superconducting quantum interference devices (SQUIDs) connected in parallel with loop areas ranging in size from 0.4 to 3.6 mu m(2). These devices are sensitive to magnetic fields parallel to the substrate and show a single antipeak from 3 to 16K with a maximum transfer function of similar to 16V/T at 3K and a field noise of similar to 110 pT/Hz(1/2) above 100 Hz at 10 K. In a second configuration, the SQIFs were made with 16 planar SQUIDs connected in parallel with loop areas ranging in size from 4 mu m(2) to 25 mu m(2) and are sensitive to the magnetic fields perpendicular to the substrate. The planar SQIF shows a single antipeak from 10 to 22K with a maximum transfer function of 7800V/T at 10K and a field noise of similar to 70 pT/Hz(1/2) above 100 Hz at 20K. Published by AIP Publishing.