Noise and Performance of Magnetic Nanosensor Based on Superconducting Quantum Interference Device

We will report results about the noise and performance of magnetic nanosensors based on niobium nano superconducting quantum interference device (nanoSQUID) having a flux capture area of 0.5 μm2. A proper device design based on a loop inductance asymmetry has been developed in order to achieve a better magnetic flux resolution. The device fabrication procedure is based on the electron-beam lithography, thin film deposition, and the lift-off technique. The characterization of the nanodevice at T =4.2 K includes measurements of current–voltage, critical current vs. magnetic flux characteristic (I−Φ), and flux noise. The nanosensors have shown a hysteretic I–V characteristic and a triangular-shaped I−Φ pattern. Due to the hysteretic behavior, the devices have been employed as a magnetic flux to current transducer. In such a configuration, an overall magnetic flux resolution of about 0.1 mΦ0 has been estimated. A proper feedback circuit has been employed to increase the dynamic range of the nanosensor. Magnetization measurements at T=4.2 K on Fe3O4 nanoparticles having a size of 8 nm have been reported, proving that nanoSQUIDs reported here can be successfully employed to investigate the magnetism at a sub-micrometric scale.