Advanced nanoSQUIDs based on sub-micron trilayer Nb/HfTi/Nb Josephson junctions

We report on the development and performance of advanced Nb nanoSQUIDs for magnetization reversal studies on individual magnetic nanoparticles (MNPs). The nanoSQUIDs are based on trilayer Nb/HfTi/Nb Josephson junctions exhibiting large critical current densities >105 A/cm2 at 4.2 K. This offers the unique advantage of combining the realization of SQUIDs with very small loop inductance, and hence ultra-low flux noise, with a superconductor multilayer approach that enables the fabrication of complex devices with significantly increased functionality for various applications. One example is the recently developed 3-axis vector nanoSQUID. This device consists of three mutually orthogonal SQUIDs (Fig.1) that allow simultaneous and independent detection of the three components of the vector magnetic moment of individual MNPs at 4.2 K in applied magnetic fields up to ~150 mT. We present the performance of improved vector nanoSQUIDs and first attempts to vectorially detect the magnetization reversal of individual Co MNPs deposited onto our devices by focused electron beam induced deposition.