ULTRA HIGH SENSITIVE THREE DIMENSIONAL SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE FOR NANOMAGNETISM APPLICATIONS

In the recent years, it has been shown that the magnetic response of nano-objects (nanoparticles, nanobead, small cluster of molecules) can be effectively measured by using a Superconducting Quantum Interference Device (SQUID) with a small sensitive area. In fact the sensor noise expressed in term of the elementary magnetic moment (Bohr magneton, µB) is linearly dependent on the SQUID loop side length. For this reason, LTc SQUIDs have been progressively miniaturized in order to improve the sensitivity up to few µB per unit of bandwidth [1]. Here, we present a very low noise three-dimensional (3D) nanoSQUID based on deep submicrometer Josepshon tunnel junctions fabricated by a Focused Ion Beam (FIB) sculpting method. Compared to typical nanoSQUIDs, the main advantages of the proposed nanosensor, are a better control of the critical current, the high modulation depth and the ultra low noise, being based on a fully reliable niobium technology. Furthermore, this 3D nanoSQUID is more reliable and robust with respect to the thermal cycles and exhibits a non-hysteretic behavior, allowing the flux locked loop operation and the employment of low readout electronics. We report the performance of the 3D nanodevice in terms of electrical transport properties and spectral density of magnetic flux and spin noise. Finally, a magnetic relaxation measurement for 6 nm magnetic nanoparticles is also reported [2], demonstrating its strength in view of nanoscale applications.