Magnetic Field Sensor Based on a Single Josephson Junction With a Multilayer Ferromagnet/Normal Metal Barrier

We report experimental studies of quantum-matter heterostructures based on a ferromagnet/normal metal multilayer proximitized by Nb superconducting electrodes to form a novel Josephson weak-link device that is highly sensitive to magnetic fields. The device is a single Josephson junction containing Al/Ni or Al/Py (Py: Ni₈₀Fe₂₀) multilayer structures, which manifests quasi-sinusoidal critical current oscillations resembling the response of a dc Superconducting Quantum Interference Device (SQUID). Our analysis shows that the field sensitivity of this novel device, as measured by the magnetic field needed to form one period of the oscillations, is about twice that reported for recent micro- or nano-SQUIDs. We present an analysis of the temperature dependence of the period of the oscillations and the Josephson critical current, as well as the background current. We believe that our devices are promising candidates for a new generation of magnetic field nanosensors.