NanoSQUIDs Based on Submicron Nb/HfTi/Nb Josephson Junctions for the Investigation of Small Spin Systems in Moderate Magnetic Fields

We report on the realization of highly sensitive dc nanoSQUIDs for the investigation of small spin systems in moderate magnetic fields. The nanoSQUIDs are based on Nb/HfTi/Nb superconductor/normal metal/superconductor Josephson junctions and patterned by e-beam lithography and chemical mechanical polishing. Low- and high-field characterization yields a stable operation in magnetic fields of up to  with rms flux noise down to . By numerical simulations based on the London equations we find an optimum spin sensitivity of .

By using a hybrid magnetometer system consisting of an Nb nanoSQUID and a Si cantilever, we investigate individual ferromagnetic nanotubes simultaneously by SQUID and torque magnetometry, which yield complementary information on magnetization reversal processes in the magnetic nanotubes.