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In the recent years, several efforts were devoted to the development of a high-sensitivity magnetic nanosensor pushing sensing capability to the individual spin level. Among the wide variety of magnetic detectors, the nano Superconducting Quantum Interference Device (nano-SQUID)seems to be the most promising sensors for nanoscale applications. In particular, during the last years a growing interest has been devoted to nanoSQUIDs, because they exhibit an ultra-high magnetic moment sensitivity (few spin or Bohr magnetons per unit of bandwidth)and allow to measure direct magnetization changes in small spin systems. The investigation of small spin clusters like molecular magnets, single electron, or cold atom clouds is a very interesting topic from both technological and scientific point of view. In fact, beside the interesting applications in information technology, nanomagnetism, medicine and biology,the study of these nanoscale systems are very attractive for their quantum mechanical properties and for future implementation in quantum computing.
Dayem bridge based nanoSQUIDs
We have developed integrated magnetic nanosensors based on a niobium dc SQUID in a washer or a coil shape with a submicron hole and two Josephson–Dayem nanobridges whose the width costriction is less than 100 nm patterned by Electron Beam Lithography (EBL). They can realized with an integrated niobium coils tightly coupled to the SQUID to easily excite the sensor in order to get the voltage-flux characteristics and to flux bias the SQUID at its optimal point. The measurements performed at liquid helium temperature shows a high voltage swing and a voltage–flux transfer coefficient (responsivity) up to 1 mV/Φ0. A very low white magnetic flux noise spectral density which results in high spin sensitivity in units of the Bohr magneton make these nanosensor suitable in magnetic detection of nanoparticles or small clusters of atoms and molecules, in the measurement of nanoobject magnetization, and in quantum computing.
Performance
Design
Main references:
An integrated superconductive magnetic nanosensor for high-sensitivity nanoscale applications
C. Granata, E. Esposito, A. Vettoliere, L. Petti, M. Russo
Nanotechnology 19 (27), 275501
Supercurrent decay in nano-superconducting quantum interference devices for intrinsic magnetic flux resolution
C. Granata, A. Vettoliere, R. Russo, E. Esposito, M. Russo, B. Ruggiero
Applied Physics Letters 94 (6), 062503
Sub-micron Josephson junction based nanoSQUID
We have also developed, in collaboration with Istituto Nazionale di Ricerca Metrologica (INRIM) an ultra high sensitive three-dimensional nano SQUID fabricated by using Focused Ion Beam (FIB) sculpting technique. Based on a fully niobium technology, the nanodevice consists in a submicrometer superconducting loop (0.2 µm2) interrupted by two nanometric Nb/Al-AlOx/Nb Josephson junctions. Thi nanodevice exhibits an intrinsic magnetic flux noise less than 1 and a corresponding spin noise sensitivity less than 10 Bohr magnetons per unit of bandwidth. It has been successfully employed in nanoparticle magnetic relaxation measurements. Due to its excellent performance, reliability, and robustness, this nanodevice offers a crucial step toward a wide employment of nanoSQUIDs in the nanoscience.
Performance
Design
Main references:
Three-dimensional spin nanosensor based on reliable tunnel Josephson nano-junctions for nanomagnetism investigations
C. Granata, A. Vettoliere, R. Russo, M. Fretto, N. De Leo, V. Lacquaniti
Applied Physics Letters 103 (10), 102602
R. Russo, C. Granata, A. Vettoliere, E. Esposito, M. Fretto, N. De Leo, E. Enrico and V. Lacquaniti
Performances of niobium planar nanointerferometers as a function of the temperature: a comparative study
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