Characterization of Superconducting Thin Films and nanoSQUIDs for Nanoparticle Investigation at High Magnetic Field

We present an experimental investigation aimed to fabricate a nanoSQUID for high-magnetic-field applications. In particular, we produced niobium films having different thicknesses (5, 10, and 15 nm) with passivation layers to investigate the transport properties of very thin niobium film in high magnetic field parallel to the film plane. The results indicate that niobium thin films are superconducting at high field; however, the passivation layers are not sufficient to avoid a degradation of superconducting properties when niobium films are cycled between room and cryogenic temperatures. We also fabricated and measured a nanosensor based on niobium nitride. Niobium nitride films have much higher magnetic critical field, and they are more stable compared with niobium ones. The characterization of the nanodevice in the temperature range from 2 to 7 K includes measurements of current-voltage and critical current versus magnetic flux characteristic. Albeit the coherence length of niobium nitride is very short compared with the niobium one, and much smaller than the Dayem bridge length, the nanoSQUIDs present modulations of critical current larger than 5% at 2 K. The modulation can be observed up to 8 T, making NbN nanoSQUIDs good candidates to measure magnetic properties of magnetic nanoparticles and nanostructures.