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Scanning electron micrograph of a niobium nanodevice including the integrated coil for the modulation, calibration and the feedback operations. The inset shows the nanoSQUID loop having an area of 0.5 μm2 and the Dayem nanobridges.
(a) Critical current as a function of the external magnetic flux (I-Φ) measured at T = 4.2 K. It is evident the curve deformation due to the inductance loop asymmetry. (b) Numerical derivative of the I-Φ curve as a function of the external magnetic field; a current responsivity increase of about five times is obtained biasing the nanoSQUID on the steepest side of the characteristic.
TEM image of iron oxide nanoparticles. The inset reports the distribution of the particle size obtained by TEM analysis; it is is well fitted by log-normal function (straight line) leading to a measured mean diameter of about 8 nm.
Scheme of the readout circuit using to excite the nanoparticles and to increase the linear dynamical range of the nanoSQUID working as magnetic flux to critical current transducer. A solenoid provides the excitation magnetic field in the same plane of the SQUID loop while an integrated coil located very close to the nanosensor acts as a feedback coil.
Magnetic field dependence of the magnetization for Fe3O4 nanoparticles measured at T = 4.2 K for a sweep magnetic field ranging from −200 to 200 G.
Magnetic relaxation measurement at T = 4.2 K of Fe3O4 nanoparticles cooled in a magnetic field of 10 mT. The red circles are relative to the nanoSQUID measurement while the blue squares are measured by a commercial system (quantum design SQUID magnetometer). The straight lines are guideline. The inset shows the same measurement in a linear scale of time.
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