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In tunnel magnetic Josephson junctions (JJs), we have provided evidence of an inverse magnetic dependence of the critical current Ic(H), i.e., a shift of the Ic(H) curves in the opposite expected direction. We have established a self-consistent method to ascribe this unconventional feature to spin polarization phenomena at the S/F interface. Through a magnetic characterization of Superconductor (S) /Ferromagnet (F) /Superconductor (S) trilayers and a magnetostatic analysis of the devices, we show that the F-stray fields fail to determine the pattern inversion. The comparative analysis with the literature supports our thesis that this phenomenon can be explained in terms of inverse proximity effect and observed with a proper choice of materials and thickness of the ferromagnetic layer involved in the junction structure. More generally, our approach proves that a careful investigation of the magnetic field pattern in magnetic JJs can lead to the detection of novel effects arising at the S/F interface.

We propose a picture for the magnetic properties of superconductor/ferromagnet (S/F) heterostructures based on Nb and permalloy $(\mathrm{Py}:{\mathrm{Fe}}_{20}{\mathrm{Ni}}_{80})$. By measuring the magnetic moment as a function of the temperature in S/F/S trilayers for different thicknesses of the middle F layer, we give evidence of the presence of a magnetic stray field of the F layer. For values of F-layer thickness below a threshold, we establish a correlation between the magnetic measurements of the S/F/S trilayers and the anomalous magnetic dependence of the critical current in S/Insulator/thin superconducting film/F/S (SIsFS) Josephson junctions (JJs). These complementary investigations provide a self-consistent method to fully characterize S/F heterostructures and possibly demonstrate effects arising from the mutual interactions between ferromagnetism and superconductivity. A shift in the Fraunhofer critical current oscillations has been observed in the opposite direction to the one commonly observed in JJs with F barriers, as it has been recently predicted by inverse and electromagnetic proximity theories. This inverse memory effect is relevant for the design of these heterostructures as memory cells and spintronic devices.

In Magnetic Josephson Junctions (MJJs) based on Superconductor-Insulator-Superconductor-Ferromagnet-Superconductor (SIS’FS), we provide evidence of an unconventional magnetic field behavior of the critical current characterized by an inverted magnetic hysteresis, i.e., an inverted shift of the whole magnetic field pattern when sweeping the external field. By thermoremanence measurements of S/F/S trilayers, we have ruled out that this uncommon behavior could be related to the F-stray fields. In principle, this finding could have a crucial role in the design and proper functioning of scalable cryogenic memories.

Liquids are the primary environments in which chemical, physical, and biological processes occur. Considering a liquid bridge as liquid unit volume (LUV) element, it is highly desirable to develop reliable tools for handling such volumes. Herein, a sort of intelligent microfluidic platform based on the pyroelectric‐electrohydrodynamics (EHD) is shown for manipulating liquid bridges and thus performing multiple functions in a flexible and simple way. Several basic operations with liquid bridges using an EHD‐pin matrix based on the pyroelectric effect engineered in ferroelectric crystals are demonstrated. By activating pyro‐EHD effect in predetermined positions (pins of the array), the locomotion and handling of single or multiple LUVs simultaneously are controlled. In particular, multiple operations such as lift, displacement, mixing, stretching, and carrying vector for microparticles, are shown. These tweezers based on a pyro‐EHD matrix can open the route for a multipurpose platform driven by physical intelligence and can be used for driving locomotion and operate manifolds functionalities in many areas of science and technology at microscale as well as nanoscale with advantages to be activated by the sole thermal stimulus, controlled remotely, and in noncontact mode.

Aim: Our aim was to describe the rearrangements of the brain activity related to genetic mutations in the SPAST gene. Methods: Ten SPG4 patients and ten controls underwent a 5 min resting state magnetoencephalography recording and neurological examination. A beamformer algorithm reconstructed the activity of 90 brain areas. The phase lag index was used to estimate synchrony between brain areas. The minimum spanning tree was used to estimate topological metrics such as the leaf fraction (a measure of network integration) and the degree divergence (a measure of the resilience of the network against pathological events). The betweenness centrality (a measure to estimate the centrality of the brain areas) was used to estimate the centrality of each brain area. Results: Our results showed topological rearrangements in the beta band. Specifically, the degree divergence was lower in patients as compared to controls and this parameter related to clinical disability. No differences appeared in leaf fraction nor in betweenness centrality. Conclusion: Mutations in the SPAST gene are related to a reorganization of the brain topology.

Direct current Superconducting QUantum Interference Device (dc SQUID) is the most sensitive magnetic flux and field detector known so far. Due to the low operating temperature and quantum working principle, a SQUID exhibits an equivalent energy sensitivity that approaches the quantum limit. Recently, great efforts have been focused to the development of nanoSQUIDs, making such a nanosensor a powerful tool to study the magnetic properties of nanoparticles at a microscopic level. This chapter focuses on nanoSQUIDs and its applications, after discussing the principles on which the SQUID is based, namely the Josephson effect and flux quantization in a superconducting ring. One of the most important factors of merit of a SQUID device is the magnetic flux noise or more precisely the spectral density of magnetic flux noise. Depending on the quantity to be measured, a suitable SQUID sensor design needs to be employed. The chapter reports on the basic principle of the main SQUID configurations.

We report results about an optimized three-dimensional nanoSQUID based on niobium tunnel nanojunctions having the loop suspended to reduce the parasitic capacitance. The SQUID loop has a size of 400 × 600 nm 2 while the dimension of the square tunnel nanojunctions is 150 × 150 nm 2 with a density of the critical current of about 35 × 10 3 A/cm 2 . The nanodevice has been characterized at liquid helium temperature; it has shown nonhysteretic current-voltage characteristics and smooth voltage- magnetic flux characteristics resulting in a very stable operation in a wide range of bias points. The spectral density of the magnetic flux noise in the white region, measured with a two-stage noise measurement setup, was as low as 300 nΦ 0 /Hz 1/2 corresponding to a spin sensitivity of few Bohr magnetons for bandwidth unit.

The theoretical understanding of Gartner's “hype curve” is an interesting open question in deciding the strategic actions to adopt in presence of an incoming technology. In order to describe the hype behaviour quantitatively, we propose a mathematical approach based on a rate equation, similar to that used to describe quantum level transitions. The model is able to describe the hype curve evolution in many relevant conditions, which can be associated to various market parameters. Different hype curves, describing the time evolution of a new technology market penetration, are then obtained within a single coherent mathematical approach. We have also used our theoretical model to describe the time evolution of the number of scientific publications in different fields of scientific research. Data are well described by our model, so we present a statistical analysis and forecasting potentiality of our approach. We note that the hype peak of inflated expectations is very smooth in the case of scientific publications, probably due to the high level of awareness and the deep preliminary understanding which is necessary to carry on a research project. Our model is anyway flexible enough to describe many patterns of increasing interest on a new idea, leading to a hype behaviour or other time evolution.

In the present paper, we will report results about experimental study of brain functional connectivity performed by using a multichannel magnetoencephalographic system based on superconducting quantum interference devices. Such quantum devices exhibit magnetic field sensitivity high enough as to measure the extremely weak magnetic signals generated by the electrical neuronal activity. This powerful tool allows to study the temporal relation of spatially neurophysiological events, i.e. the functional connectivity, which recently captured attention in the field of brain function exploration. The paper reports system and sensors performance as well as data acquisition system and a detailed pipeline data analysis will be described. Brain connectivity measurements relative to parents of children with autism spectrum disorder will be shown, highlighting the preliminary results in topological metrics for different sub-items of autism-spectrum quotient test.

Josephson junctions (JJs) containing ferromagnetic (F) materials are being considered for applications as cryogenic random access memories (RAM). In this work, we report on the fabrication and characterization of tunnel JJs, based on Nb technology with a strong ferromagnetic interlayer Ni80Fe20 alloy (Permalloy), which is suitable for the realization of devices with reduced area and guarantees relative low saturation and coercive fields in the use of JJs as RAM elements. We have successfully realized Josephson memory elements that work well down to 7 mu m(2) preserving high values of the characteristic voltage. We have also investigated the role of the F layer thickness, and by measuring the critical current dependence on the external applied magnetic field, we have optimized our devices as memory elements using thin ferromagnetic layers with thickness down to 3nm. We have experimentally proved their functioning as memory elements by applying magnetic field pulses in opposite directions that can change the F layer magnetization.

The unique deformability and the compliance ability of thin sheets on soft substrates attract much interest for studying the phenomena related to elastic instabilities as well as for sensing very weak forces such as those generated by live cells in vitro. However, the techniques used currently for producing such platforms are affected by a high degree of complexity and poor repeatability. Moreover, their deformability is usually used as a passive response to the action of an external force. Herein we propose a novel concept for a reliable and dynamic skin-over-liquid system made of a periodic array of highly compliant microbumps actuated through electrode-free electrohydrodynamic (EHD) pressure. We demonstrate that these structures are highly repeatable and capable of swelling and deflating easily under a simple thermal stimulation driven by the pyroelectric effect, thus providing a challenging platform that can be actively controlled at the microscale. Furthermore, we show the proof of principle by swelling these microbumps for mechanically stimulating live cells in vitro, thus opening the route to more reliable and easy to accomplish assays in the field of mechanobiology. Researchers curious about how mechanical stress impacts cell growth can now turn to silicone plastics that grow microbumps on demand. Simonetta Grilli from Italy’s Institute of Applied Sciences and Intelligent Systems in Pozzuoli and colleagues created a controllable ‘skin-over-liquid’ system by coating a silicone polymer solution onto lithium niobate, a crystal that contains patterned regions of electric charge. An initial plasma treatment produced a flat stiff film on top of the liquid silicone. Thermal heating caused the skin to swell and form dimpled, air mattress-like patterns, corresponding to the underlying lithium niobate domains. Removal of heat restored the sheet to its initial state. The chemically inert skin supported live fibroblast cells and was used to determine reactions to mechanical stress. Significant variations in nuclei and cytoskeletons were observed between cells grown under flat or swollen-skin conditions. We propose an innovative skin-over-liquid system made of a periodic array of highly compliant microbumps actuated through an electrode-free electrohydrodynamic (EHD) pressure. We demonstrate that these structures are highly repeatable and are capable to swell and deflate easily under a simple thermal stimulation driven by pyroelectric effect, thus providing a challenging platform that can be actively controlled at microscale. We show the proof of principle by swelling these microbumps for stimulating mechanically live cells in vitro, thus opening the route to more reliable and easy to accomplish assays in the field of mechanobiology.

The critical current value is a key parameter of a Superconducting Quantum Interference Device. In this paper we investigate the effects of different critical current values on the noise performance of SQUID magnetometers. By using a statistical-like approach, we measure the spectral density of magnetic field noise of 200 magnetometers relating the values to the critical current change. The magnetometer consists of a dc-SQUID in a washer shape magnetically coupled to a square superconducting pickup coil. The fully integrated design includes a feedback coil to work in Flux Locked Loop mode and an Additional Positive Feedback circuit to increase its voltage responsivity. The main application field of these sensors is the magnetoencephalography that exploits multichannel systems based on SQUID magnetometers, in which the uniformity of noise performance of the sensors is needed. We found that a best value of critical current is 20 ?? and also that a value spread ranging from 8 to 40 ?m, does not affect in an evident way the sensitivity of such magnetometers. The corresponding noise spectral density remains within the range 2 - 6 fT/Hz.

Recently it has been proven that the magnetic response of magnetic nano-objects such as nanoparticles, nanobeads, and small cluster of molecules can be effectively measured by using a Superconducting Quantum Interference Device (SQUID) with a small sensitive area. Here, we present a high sensitivity nanoSQUID based on deep submicrometer Josephson tunnel junctions fabricated by a Focused Ion Beam (FIB) sculpting method. The nanosensor consists of a niobium superconducting loop (0.4 × 1.0 ?m^2) interrupted by two sandwich nanojunctions (Nb/Al-AlOx/Nb) having an area of about (300 × 300) nm^2. An experimental investigation of the main characteristics of such nanodevice as a function of the temperature is presented.

Micro and nano-sized Superconducting Quantum Interference Devices (SQUIDs) allow the measurements of extremely low magnetic moment. In the last decade, many efforts have been devoted to the study and the development of these quantum sensor at a nanometric scale (nanoSQUIDs). In the present work a study of performance of these nanosensors in different configurations is presented. In particular, the magnetic flux coupling and the spin sensitivity have been computed for planar nanoSQUIDs in square and rectangular shape in presence of an elementary magnetic moment (Bohr magneton). The computation has been carried out as a function of the position of the Bohr magneton within the sensitive SQUID loop and for different distances from the loop plane. The same characteristics have been also computed for a square nanoSQUID as a junction of side length taking into account the increase of the magnetic flux noise as a function of the loop inductance. In addition a configuration including a non-flat geometry has been analyzed.

The magnetic field dependence of the Eck step voltage in long Josephson tunnel junctions (LJTJs) can be exploited for ultralow-noise magnetic sensing. The magnetic flux to be measured is captured by a non-interrupted superconducting pickup loop in which a narrow constriction, forming the LJTJ wiring layer, produces a local high density circulating currents which, in turn, induces a magnetic field large enough to set a biased LJTJ at a finite voltage proportional to the field strength (flux-flow state). On this basis, an innovative and ultralow-noise superconducting device has been realized having a highly linear voltage responsivity and an intrinsic voltage spectral density down to few pV/ $\surd $ Hz. Being that the intrinsic voltage fluctuations of these all-Niobium sensors are very low (at $T = 4.2$ K), a double transformer superconducting quantum interference device (SQUID) amplifier has been used to determine the amplitude of its voltage spectral density obtaining a value as low as 10 pV/ $\surd $ Hz. In addition, the 1/ ${f}$ noise does not affect the sensor performance down to a few hertz. The corresponding magnetic field noise, equal to 10 fT/ $\surd $ Hz, together with highly linear and broadband voltage responsivity over a wide magnetic flux range, features performances that are comparable with those of a SQUID magnetometers having a comparable flux capture area.

We present an experimental investigation of nanoSQUIDs based on niobium nitride films. Niobium nitride has a relatively high critical temperature and a large upper critical magnetic field, making it a good material for superconducting electronics working in high magnetic field. We have fabricated nanoSQUIDs using electron beam lithography lift-off technique and deposition of niobium nitride films by magnetron sputtering at room temperature. The characterization of nanoSQUIDs was performed at 4.2 K and it consists mainly of current-voltage (IV) characteristics and critical current as a function of external magnetic field (magnetic pattern). The fabricated nanoSQUIDs show a hysteretic IV characteristic and they present a multi-values magnetic pattern. We show that by reducing the critical current by ion etching it is possible to obtain nanoSQUIDs with a single value magnetic pattern suitable for magnetic particle measurements. Magnetic noise analysis has been performed and a white noise of 0.3 ??0/ sqrt(Hz) has been estimated.

Integrated magnetic sensors based on niobium dc SQUID (Superconducting Quantum Interference Device) for nanoparticle characterizations are presented. The SQUIDs consists of two Dayem bridges of 90 nm × 250 nm and loop area of 4, 1, and 0.55 μm2. The devices are realized by using an e-beam lithography nano-fabrication process which can directly pattern the devices in an electron-positive resist and then transferred to a 20 nm single niobium layer by a lift-off post-process. The SQUIDs were designed to have a hysteretic current–voltage characteristic in order to work as a magnetic flux-current transducer. The presence of an integrated niobium coil, tightly coupled to the SQUID, allows us to easily excite the SQUID and to flux bias the SQUID at its optimal working point. Current–voltage characteristics, critical current as a function of the external magnetic field and switching current distributions were performed at liquid helium temperature. A critical current modulation of about 20% and a current-magnetic flux transfer coefficient (responsivity) of 30 μA/Φ0 have been obtained, resulting in a magnetic flux resolution better than 1 mΦ0. The authors performed preliminary measurements with and without iron oxide nanoparticles on the SQUID loop in order to show the device sensitivity in view of nano-magnetism applications. It was showed that the presence of magnetic nanoparticles can be easily detected and the magnetic relaxation curve measured.

Magnetometers based on Superconducting Quantum Interference Device (SQUID) are widely employed in high sensitivity magnetometry. In particular, new multichannel systems for biomagnetic applications require many sensors which are very close to each other giving the crosstalk disturbance between the neighboring channel. Here, we present experimental results about a fully integrated dc-SQUID magnetometer, based on niobium technology, having a suitable design which allows to reduce crosstalk due to both the feedback coil and wires. The crosstalk level measurements relative to a particular arrangement of sensors are reported. In such configuration, four magnetometers are placed over a square board 30 mm in side with a distance between their sensor centers of 14 mm. The measurements have been performed in a 4 He cryostat at T = 4.2 K in a flux-locked loop configuration using a readout electronics with a direct coupled scheme. The experimental data have shown a substantial reduction of crosstalk among neighboring sensors with respect to a traditional feedback coil. Furthermore, the field noise measurements have ensured that the new pickup and feedback coils design does not introduce any noise level degradation.

Measurements and noise performances of integrated nano superconducting quantum interference devices (nano-SQUIDs) are presented. The nano-sensors are based on nanometric niobium constrictions (Dayem bridges) inserted in a square loop having a side length of 200 nm. Integrated micrometric niobium coils located close to the sensor allow both an easy tuning/calibration and the optimization of the working point. Improved measurements of voltage-flux characteristic, flux to voltage transfer factor and noise performances are reported. In small signal mode, the sensors have shown a magnetic flux noise spectral density of 1.5 muPhi0/Hz1/2. Furthermore, preliminary measurements concerning the critical current vs. temperature dependence and the switching probability of the critical current are shown.

In this paper a nanofabrication process, based on a focused ion beam (FIB) nanosculpting technique, for high sensitivity three-dimensional nanoscale superconducting quantum interference devices (nanoSQUIDs) is reported. The crucial steps of the fabrication process are described, as are some peculiar features of the superconductor–normal metal–insulator–superconductor (SNIS) Josephson junctions, which may useful for applications in cryocooler systems. This fabrication procedure is employed to fabricate sandwich nanojunctions and high sensitivity nanoSQUIDs. Specifically, the superconductive nanosensors have a rectangular loop of 1 × 0.2–0.4 μm2 interrupted by two square Nb/Al–AlO x /Nb SNIS Josephson junctions with side lengths of 0.3 μm. The characterization of a typical nanoSQUID has been carried out and a spectral density of magnetic flux noise as low as 0.8 μΦ0 Hz–1/2 has been measured.

We present an experimental investigation aimed to fabricate a nanoSQUID for high-magnetic-field applications. In particular, we produced niobium films having different thicknesses (5, 10, and 15 nm) with passivation layers to investigate the transport properties of very thin niobium film in high magnetic field parallel to the film plane. The results indicate that niobium thin films are superconducting at high field; however, the passivation layers are not sufficient to avoid a degradation of superconducting properties when niobium films are cycled between room and cryogenic temperatures. We also fabricated and measured a nanosensor based on niobium nitride. Niobium nitride films have much higher magnetic critical field, and they are more stable compared with niobium ones. The characterization of the nanodevice in the temperature range from 2 to 7 K includes measurements of current–voltage and critical current versus magnetic flux characteristic. Albeit the coherence length of niobium nitride is very short compared with the niobium one, and much smaller than the Dayem bridge length, the nanoSQUIDs present modulations of critical current larger than 5% at 2 K. The modulation can be observed up to 8 T, making NbN nanoSQUIDs good candidates to measure magnetic properties of magnetic nanoparticles and nanostructures.

In this paper, an experimental investigation of the main characteristics of a niobium nano Superconducting QUantum Interference Device (nanoSQUID) as a function of the temperature (9-0.3 K) is presented. The nanosensor consists of a niobium superconducting loop (0.4 × 1.0μm2) interrupted by two sandwich nanojunctions (Nb/Al-AlOx/Nb) having an area of about (300 × 300) nm2. These nanodevices have been fabricated by means of a focused ion beam sculpting method, which is used as a lithographic technique to define the various elements of the SQUID. We have performed measurements of current-voltage, critical current-magnetic flux characteristics, and switching current distributions from the zero voltage state for different temperatures. The high critical current modulation depths and the low intrinsic dissipation exhibited by these devices ensure a suitable sensitivity for nanoscale applications in the whole temperature range investigated.

The magnetic sensing at nanoscale level is a promising and interesting research topic of nanoscience. Indeed, magnetic imaging is a powerful tool for probing biological, chemical and physical systems. The study of small spin cluster, like magnetic molecules and nanoparticles, single electron, cold atom clouds, is one of the most stimulating challenges of applied and basic research of the next years. In particular, the magnetic nanoparticle investigation plays a fundamental role for the modern material science and its relative technological applications like ferrofluids, magnetic refrigeration and biomedical applications, including drug delivery, hyper-thermia cancer treatment and magnetic resonance imaging contrast-agent. In this framework, several efforts have been devoted to the development of a high sensitivity magnetic nanosensor pushing sensing capability to the individual spin level. Among the different magnetic sensors, Superconducting QUantum Interference Devices (SQUIDs) exhibit an ultra high sensitivity and are widely employed in numerous applications. In the recent years, it has been proved that the magnetic response of nano-objects can be effectively measured by using a SQUID with a very small sensitive area (nanoSQUID). In fact, the sensor noise, expressed in terms of the elementary magnetic moment (spin or Bohr magneton), is linearly dependent on the SQUID loop side length. For this reason, SQUIDs have been progressively miniaturized in order to improve the sensitivity up to few spin per unit of bandwidth. With respect to other techniques, nanoSQUIDs offer the advantage of direct measurement of magnetization changes in small spin systems. In this review, we focus on nanoSQUIDs and its applications. In particular, we will discuss the motivations, the theoretical aspects, the fabrication techniques, the different nanoSQUIDs and the relative nanoscale applications., 145 page, 59 figures, Review article

We present a fully integrated rf SQUID-based system as flux qubit with a high control of the flux transfer function of the superconducting transformer modulating the coupling between the flux qubit and the readout system. The control of the system is possible by including into the superconducting flux transformer a vertical two-Josephson-junctions interferometer (VJI) in which the Josephson current is precisely modulated from a maximum to zero by a transversal magnetic field parallel to the flux transformer plane. The proposed system can be also used in a more general configuration to control the off-diagonal terms in the Hamiltonian of the flux qubit and to turn on and off the coupling between two or more qubits.

We present a niobium-based Josephson device as prototype for quantum computation with flux qubits. The most interesting feature of this device is the use of a Josephson vertical interferometer to tune the flux qubit allowing the control of the off-diagonal Hamiltonian terms of the system. In the vertical interferometer, the Josephson current is precisely modulated from a maximum to zero with fine control by a small transversal magnetic field parallel to the rf superconducting loop plane. © 2006 IOP Publishing Ltd.

In the recent years, it has been shown that the magnetic response of nano-objects (nanoparticles, nanobeads, and small cluster of molecules) can be effectively measured by using a Superconducting Quantum Interference Device (SQUID) with a small sensitive area. Here, we present high sensitivity nanoSQUIDs based on deep submicrometer Josephson tunnel junctions fabricated by a Focused Ion Beam (FIB) sculpting method. Two different configuration have been realized: a vertical configuration where the nanosensor loop is perpendicular to the substrate plane and a planar one having the SQUID loop parallel to the substrate plane. In both configurations the flux capture and the junction areas are 0.2 and 0.09 μm 2 , respectively. At liquid helium temperature the nanosensor have shown non-hysteretic current-voltage characteristics and large voltage modulation depths as well as high voltage responsivities. A spectral density of magnetic flux noise as low as 700 nΦ 0 /Hz 1/2 has been measured in small signal mode using a low noise direct coupling electronics. The computed spin sensitivity has provided a value less than 10 Bohr magneton per bandwidth unit.

The ultra high sensitivity exhibited by Superconducting Quantum Interference Device (SQUIDs) could be the key to explore new field of nanoscience such as the investigation of small cluster of elementary magnetic moments. In this paper, an ultra high sensitive niobium nanoSQUID based on submicron Josephson tunnel junction is presented. It has been fabricated in a vertical configuration by using a three-dimensional focused ion beam sculpting technique. In such a configuration, the nanosensor loop (area of 0.25 μm 2 ) is perpendicular to the substrate plane allowing to drastically reduce the spurious effects of the external magnetic field employed to excite the nano-objects under investigation. Main device characteristics have been measured at T =4.2 K by using a low noise readout electronics. Due to high voltage responsivity, the nanosensor has exhibited a spectral density of the magnetic flux noise as low as 1.6 μΦ 0 /Hz 1/2 .

We report the performance of a reliable three-dimensional nanometer-sized Superconducting QUantum Interference Device (SQUID). The use of superconductor-isolator-superconductor Nb/Al-AlOx/Nb Josephson tunnel junctions together with small SQUID loop dimensions permits a high modulation depth of the SQUID's critical current and thus leads to very low intrinsic flux noise of the device. In particular, we present electrical characterization including detailed noise investigations. At 4.2 K, two-stage noise measurements with a SQUID as a low noise preamplifier result in a white flux noise of 51 nU0/Hz1/2, which is equivalent to an energy resolution of 1.3 h, with h being Planck's constant. Simulation of spin sensitivities results in about 1 lB/Hz1/2 for an electron spin positioned directly above the SQUID ring.

A fully integrated low noise superconducting quantum interference device (SQUID) in a magnetometer configuration is presented. An intrinsic high voltage responsivity as high as 500 muV/Phi0 has been obtained by introducing a resonance in the voltage - magnetic flux characteristic. This resonance is induced by an integrated superconducting coil surrounding the pick-up coil and connected to one end of the SQUID output. The SQUID magnetometer exhibits a spectral density of magnetic field noise as low as 3 fT/Hz(1/2). In order to verify the suitability of the magnetometer, measurements of bandwidth and slew rate have been performed and compared with those of the same device without the resonance and with additional positive feedback. Due to their good characteristics such devices can be employed in a large number of applications including biomagnetism.

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.

The low-current fluctuations at cryogenic temperatures together with the low dynamical resistance in the resonant states of Josephson tunnel junctions allow for the realization of superconducting oscillators up to the THz range with ultra-low spectral linewidth. By virtue of the Josephson frequency-voltage relationship, we show that the same properties can be exploited for the practical realization of magnetic flux-to-voltage transducers based on the flux?flow in long Josephson tunnel junctions whose intrinsic low-frequency voltage fluctuations at amount to few , that is, too small to be measured by any present semiconductor electronics. Nevertheless, by using a double transformer SQUID amplifier we demonstrate that the (amplitude) voltage spectral density, , of an all-niobium sensor does not exceed the level of and is not affected by excess noise at least down to few hertz. Such ultra-low white noise, corresponding to a magnetic field noise , together with a highly linear and broadband voltage responsivity over a wide magnetic flux range, makes the flux?flow magnetometers potentially competitive with SQUID-based devices.

The nanosuperconducting quantum interference device (nanoSQUID) is a powerful tool for nanoscience investigations. In this paper, the main features of niobium nanoSQUID based on deep submicron Josephson tunnel junctions have been investigated. The superconductive nanosensor has a rectangular loop of (1 × 0.4 μm 2) interrupted by two square Josephson junctions having a side length of 0.3 μm. The crucial steps of the fabrication process have been performed using focusing ion beam (FIB) nanosculpting technique. A full characterization of the nanosensor has been performed including the measurement of the voltage swing, the voltage responsivity, the spectral density of the magnetic flux and spin noise and the investigation of the main characteristics as a function of the temperature. Due to a very high responsivity (2.9 mV/ Φ0), the nanodevice exhibited, at T= 4.2 K, an intrinsic spectral density of the magnetic flux as low as 600 n Φ0/Hz 1/2, corresponding to a magnetic moment noise of 9 μB/Hz 1/2. For temperature less than 4.0 K, the nanodevice shows hysteretic current-voltage characteristics. However, the high critical current modulation depths ensure a suitable sensitivity for nanoscale applications.