Superconducting Quantum Interferometer Device Research Articles

A Superconducting Micro-Magnetometer for Quantum Vortex in Superconducting Nanoflakes.

Superconducting quantum interferometer device (SQUID) plays a key role in understanding electromagnetic properties and emergent phenomena in quantum materials. The technological appeal of SQUID is that its detection accuracy for the electromagnetic signal can precisely reach the quantum level of a single magnetic flux. However, conventional SQUID techniques normally can only be applied to a bulky sample and do not have the capability to probe the magnetic properties of micro-scale samples with small magnetic signals. Herein, it is demonstrated that, based on a specially designed superconducting nano-hole array, the contactless detection of magnetic properties and quantized vortices in micro-sized superconducting nanoflakes is realized. An anomalous hysteresis loop and a suppression of Little-Parks oscillation are observed in the detected magnetoresistance signal, which originates from the disordered distribution of the pinned vortices in Bi2 Sr2 CaCu2 O8+δ . Therefore, the density of pinning centers of the quantized vortices on such micro-sized superconducting samples can be quantitatively evaluated, which is technically inaccessible for conventional SQUID detection. The superconducting micro-magnetometer provides a new approach to exploring mesoscopic electromagnetic phenomena of quantum materials.

Manganese-doped titania matrix obtained by sol-gel process: Magnetic properties

The search for materials that can bear the increasingly abrupt conditions imposed to electronic devices in computers and other systems has intensified. Materials that are sensitive to variations in magnetic fields and resistant to sharp variations in temperature are desirable. To achieve such materials, several sample preparation methods have been employed. Most of these methods rely on the mechanical systems of mixtures and usually require significant discharge temperatures. In particular, the sol-gel method is quite promising because it allows for direct control of the structure and morphology of the material in all stages of the synthetic procedure. In this study, we have doped a titanium oxide matrix with manganese chloride, which afforded a material with a paramagnetic phase. Results from our investigation into the relationship between magnetic susceptibility and temperature, obtained from measurements in a superconducting quantum interferometer device (SQUID), pointed to the great sensitivity of the prepared material to low-intensity magnetic fields for temperature.

Optical and magnetic characterizations of zinc substituted copper ferrite synthesized by a co-precipitation chemical method

Nano-sized Cu1-xZnxFe2O4(x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1) ferrites were synthesized by a co-precipitation chemical method. The structural, morphological, optical and magnetic properties of the products were determined and characterized in detail by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission scanning electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and superconducting quantum interferometer device (SQUID). X-ray analysis showed that all compositions crystallize with a cubic spinel-type structure with an average crystallite size in the range of 11–13 nm. The lattice parameter increased from 8.331 to 8.400 Å with increasing Zn content. The optical properties of the nanoferrites were investigated by UV–vis spectroscopy and photoluminescence (PL) spectra. UV–vis absorption spectra show that the energy band gap (Eg) of Zn-doped copper ferrite decreases from 3.64 to 3.10 eV with increasing the particle size. The broad visible emission band is observed in the entire PL spectrum. The Cu1-xZnxFe2O4 nanoferrites exhibit superparamagnetic behavior at room temperature (RT). The saturation magnetization (Ms) varies considerably with Zn content to reach a maximum value for Cu0.4Zn0.6Fe2O4 composition, i.e.74.65 emu/g. The high Ms and magnetic moment values are attributed to cation distribution change.

Surface modification of graphene oxide sheets on magnetic particles for magnetic paper

Magnetic paper manufactures are nowadays widely used in information storage, electromagnetic shielding and security industry for its outstanding performances. In this article, Tb-doped germanium borosilicate glass was prepared by melt quenching technique and they were used as magnetic sources of magnetic paper to loading into the bamboo fibers. Magnetic paper has been successfully produced by adding inorganic magnetic particles modified by different concentrations of graphene oxide (GO) solution. The samples were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Raman Spectroscopy, Superconducting Quantum Interferometer Device (SQUID) and Scanning Electron Microscope (SEM). The results shown that the structure of magnetic particle are made from [BO3], [BO4], [A1O6], [SiO4] and [GeO4]. GO sheets had been successfully immobilized on magnetic particles (MPs) surface via electrostatic interaction. SQUID indicated that the magnetic particles and papers were paramagnetic materials. SEM images clearly shown that the MPs loaded into the lumen of bamboo fibers and the interstitial of fibers. Bridge-fibers that connecting other cellulose fibers and MPs by hydrogen bonds were formed in the network of paper due to the functional groups on surface of magnetic particles. The mechanical properties of papers increased with the increment of GO concentration, which is correlated with the hydrogen-bonding that forming by bridge-fibers and other cellulose fibers in network of paper.

Room temperature ferrimagnetism and low temperature disorder effects in zinc ferrite thin films

Zinc ferrite is a normal spinel and antiferromagnetic in nature with a Neel temperature of 10K in the micron regime. It exhibits interesting features like superparamagnetism, spin glass and ferrimagnetism in the nano-regime. These anomalies make zinc ferrite striking among various other spinels. Further, in the thin film form, the magnetic properties are dependent on preparative techniques, annealing and deposition parameters. In the present work, zinc ferrite thin films were prepared by RF sputtering. The films were annealed at 400°C and 600°C. The thickness and composition of films were estimated by employing Rutherford Backscattering Spectrometry (RBS). The structural and microstructural studies conducted using Glancing X Ray Diffractometer (GXRD) and Transmission Electron Microscope (TEM) indicates the formation of a spinel phase and grain growth was observed with annealing. Magnetic measurements were carried out using a Superconducting Quantum Interferometer Device–Vibrating Sample Magnetometry (SQUID VSM). The films were found to be ferrimagnetic at room temperature and Field Cooling–Zero Field Cooling (FC–ZFC) studies indicate the presence of disorders.

Hollow Iron Oxide Nanoparticles in Polymer Nanobeads as MRI Contrast Agents

Magnetic nanobeads are synthesized by coprecipitation of hollow iron oxide nanoparticles and an amphiphilic polymer. The resulting nanobeads can be tuned in diameter and nanoparticle content. X-ray absorption near-edge structure (XANES) spectroscopy and superconducting quantum interferometer device (SQUID) characterization of the nanobeads reveal that they exhibit an increased effective magnetic anisotropy as compared to the individual nanoparticles, despite that no structural changes of the particles had occurred during the embedding process into the polymer. The spin–spin relaxation times of the pristine hollow nanoparticles and of the final magnetic nanobeads reveal a high R2 relaxivity of 206 s–1 mM–1 for the magnetic nanobeads. This result should enable their application as negative contrast enhancing agents in magnetic resonance imaging.

Experimental analysis of the measurement strength dependence of superconducting qubit readout using a Josephson bifurcation readout method

We succeeded in controlling the measurement strength of a macroscopic quantum system, namely a persistent current quantum bit (qubit), by using a transmission line type Josephson bifurcation amplifier (JBA: an ac-driven superconducting quantum interferometer device) as a probe. By employing a special pulse sequence, we found that the weighted average of the Ramsey fringe visibility (α-value) can be used as an indicator of quantum state projection. The sudden change in the α-value magnitude at around the threshold suggests that an entangled state of the qubit–JBA composite system settles in one of the two possible classically correlated qubit–JBA states caused by strong decoherence. This is an important result in terms of understanding the mechanisms of quantum state measurement.

Optical and magnetic properties of Fe-doped ZnO nanoparticles prepared by the sol-gel method

Fe-doped ZnO nanoparticles were prepared in a solvo-thermal via sol-gel process by base-catalysed hydrolysis of zinc acetate with doping concentrations from 2 up to 5% Fe. The structural, magnetic and optical properties of the samples were studied by using X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, superconducting quantum interferometer device (SQUID) and UV-VIS spectroscopy. A reduction in particle size was shown with increase in the dopant (Fe) concentration in ZnO. The Fe-doped ZnO samples possess ferromagnetism at room temperature with significant changes in M-H loop with increasing doping concentration. The hysteresis loops reveal that the saturation magnetisation Ms and the coercivity Hc for 2% Fe and 5% Fe-doped ZnO are 2.29 emu/g, 3.91 emu/g, 671 Oe and 659 Oe, respectively. The optical properties were determined by UV-vis spectroscopy and photoluminescent spectroscopy. In this study, the optical band gap of ZnO nanoparticles increased from 3.5 eV to 3.71 eV when the Fe concentration was increased up to 5%. In the present work, the optical and magnetic properties of Fe doped ZnO nanoparticles are improved by a sol gel method.

Optical and magnetic properties of Zn0.98Mn0.02O nanoparticles

Pure and Mn-doped colloidal ZnO particles were prepared in a solvo-thermal via sol–gel process by base-catalyzed hydrolysis of zinc acetate. We have studied the structural, magnetic and optical properties of the samples using X-ray diffraction (XRD), transmission electron microscopy, energy dispersive X-ray analysis, superconducting quantum interferometer device and UV–Vis spectroscopy. The XRD spectra show that all the samples are hexagonal wurtzite structures. The calculated average particle size of the samples was approximately 7–3 nm, indicating that the particle size decreased by doping with manganese. Magnetic investigations showed that at room temperature the Mn-doped ZnO possessed ferromagnetism with the saturation magnetic moment of 0.194 emu/g. The room temperature PL measurements illustrate UV-emission centered at 351 nm (3.53 eV), which is ascribed to the near-band-edge emissions of ZnO, violet emission at 512 nm (2.42 eV). The UV–Vis spectra showed a blue-shift from 3.42 to 3.78 eV when the ZnO doped with manganese.

Magnetic susceptibility of (Bi2 − x Sb x )Te3 (0 < x < 1) alloys in the temperature range 2 to 50 K

The superconducting quantum interferometer device with Josephson junctions (SQUID magnetometer) is used to study the temperature dependences of the magnetic susceptibility of (Bi2−x Sb x )Te3 (0 < x < 1) alloy crystals in the temperature range 2 to 50 K, at the magnetic field vector H orientations H | C 3 and H ⊥ C 3 with respect to the crystal trigonal axis C 3. It is found that the magnetic susceptibility of the ion core of the samples under study is χ G = −0.35 × 10−6 cm3/g, the contribution of lattice defects to magnetic susceptibility can be disregarded, and the contribution of free carriers is of a diamagnetic nature in the entire studied temperature range. It is shown that the contribution of free carriers to the resulting magnetic susceptibility and its anisotropy can be described within the Pauli and Landau-Peierls approach. In calculating the magnetic susceptibility, taking into account the constant concentration of free carriers in the state of pronounced degeneracy, it is found that the temperature dependence of the anisotropic effective masses varies with crystal chemical composition. This is possibly associated with the complex structure of the valence band and its variation as the Sb2Te3 content in the alloy increases.

On mathematical methods to improve imaging of vortices using scanning superconducting quantum interferometer device (SQUID) microscope

The spatial resolution of scanning superconducting quantum interference device (SQUID) microscope, which is considered naively to be limited by the size of the pickup coil (typically greater than of the order of μm), can be improved by applying a mathematical transformation to the obtained data. The resolution of the image is expected to be improved to the scanning step size (can be less than of the order of μm). In reality the presence of the noise may lead to unexpected reduction of quality of images. Problems to be solved, in applying the method to visualize the fluxons in superconducting network structures, include the proper choice of filter to remove noise contributions. Examples of results of numerical simulations and of analysis of real experimental data are presented. Discussions are given on boundary problem which may arise in observations in superconducting network samples.

Magnetic Properties of Synthetic Eumelanin—Preliminary Results†

We report an experimental and theoretical study of magnetic properties of synthetic eumelanin. The magnetization curves are determined by using both a vibrating sample magnetometer and a superconducting quantum interferometer device in an extended range of magnetic fields ranging from -10 kOe to 10 kOe at different temperatures. We find that the eumelanin magnetization can be qualitatively explained in terms of a simple model of dipolar spheres with an intrinsic magnetic moment. The latter one is experimentally measured by using X-band electron paramagnetic resonance. Our findings indicate that synthetic melanins are superparamagnetic.

Proton-induced magnetic order in carbon: SQUID measurements

In this work we have studied systematically the changes in the magnetic behavior of highly oriented pyrolytic graphite (HOPG) samples after proton irradiation in the MeV energy range. Superconducting quantum interferometer device (SQUID) results obtained from samples with thousands of localized spots of micrometer size as well on samples irradiated with a broad beam confirm previously reported results. Both, the para- and ferromagnetic contributions depend strongly on the irradiation details. The results indicate that the magnetic moment at saturation of spots of micrometer size is of the order of 10−10emu.

A planar picoamperemeter based on a superconducting quantum interferometer

An optimized picoamperemeter based on a superconducting quantum interferometer device (SQUID) for a metal cold-electron bolometer is fabricated and experimentally studied. The intrinsic SQUID current noise caused by the input coil is estimated to be less than 1 pA/Hz1/2. Owing to the application of modulation electronics, current sensitivity in the input coil reaches 5 pA/Hz1/2 in the frequency band from 10 Hz to 10 kHz.

Preparation and Characterization of Ultrafine Co and Ni Particles in a Polymer Matrix

A facile route for in situ synthesis of Co and Ni nanoparticles in a preorganized polyacrylamide gel is reported. Metal-polymer composites were prepared by gamma-irradiation at room temperature. The Co nanoparticles were roughly 3-5 nm in size and were stable in the polymer matrix in the presence of air. The presence of Co and Ni nanoparticles was established by their ability to transfer an electron to methyl viologen {paraquat: 1,1'-dimethyl 4,4'-dipyridinium dichloride; MV(2+) (Cl(-))(2)}. The Co and Ni nanoparticles were probed for their magnetic characteristics by a superconducting quantum interferometer device (SQUID) magnetometer and display a low superparamagnetic blocking temperature T(B) of about 13 and 10 K, respectively. The field-dependent magnetic behavior below T(B) displays the standard features corresponding to superparamagnetism, as expected for very small Co and Ni crystallites. This also suggests that particles are polycrystalline in nature.

Synthesis, structure and spectroscopy of new thiopyrone and hydroxypyridinethione transition-metal complexes

The coordination chemistry of several O,S mixed donor ligands, namely thiopyrone and hydroxypyridinethione chelators, with a variety of middle and late first-row transition-metal ions is described. Complexes of 3-hydroxy-2-methyl-4-thiopyrone (thiomaltol) with cobalt(II), copper(II) and zinc(II); 3-hydroxy-1,2-dimethyl-4(1H)-pyridinethione (3,4-HOPTO) with iron(III), nickel(II), copper(II) and zinc(II); and 3-hydroxy-1-methyl-2(1H)-pyridinethione (3,2-HOPTO) with iron(III), nickel(II), copper(II) and zinc(II) have been synthesized and characterized. The structures, absorbance spectroscopy, cyclic voltammetry and superconducting quantum interferometer device (SQUID) measurements of selected metal complexes, as well as ligand protonation constants, are reported. Most of the metal complexes show coordination geometries indicative of a strong trans influence by the O,S chelators. The data presented herein provide the most detailed study of the transition-metal coordination chemistry of both thiopyrone and hydroxypyridinethione O,S donor ligands to date, and provide the basis for the investigation of these ligands in realm of biological inorganic chemistry.

Peculiar magnetic and electrical properties near structural percolation in metal-insulator granular layers

We study CoFe∕Al2O3 multilayers, varying from granular to continuous structure with CoFe nominal thickness (10Å⩽t⩽18Å). Structural percolation takes place at t=tc≈18Å, changing from activated to metallic conductance. A sharp anomaly in ac coercivity of magneto-optical Kerr effect and in magnetization M by superconducting quantum interferometer device is found at t=t*≈17Å, interpreted as transition from superferromagnetism (by dipolar coupled CoFe clusters) to exchange ferromagnetism. Onset at t=t* of anisotropic magnetoresistance (AMR) is attributed to skew scattering of bandlike electrons within giant fractal clusters. These structures may cause the observed Barkhausen noises in M and AMR at t≈t*, disappearing at t&amp;gt;t*.

Induced magnetic ordering by proton irradiation in graphite.

We provide evidence that proton irradiation of energy 2.25 MeV on highly oriented pyrolytic graphite samples triggers ferro- or ferrimagnetism. Measurements performed with a superconducting quantum interferometer device and magnetic force microscopy reveal that the magnetic ordering is stable at room temperature.

Growth and characterization of single crystalline NiMnSb thin films and epitaxial NiMnSb/MgO/NiMnSb(001) trilayers

NiMnSb(001) high-quality epitaxial thin films have been prepared by molecular-beam epitaxy. The growth and morphology of the films have been extensively studied using electron diffraction and scanning tunneling microscopy. We report the presence of various surface structures on the free NiMnSb(001) surface. The structural properties of the prepared single-crystalline NiMnSb films have been analyzed by transmission electron microscopy and x-ray absorption. The typical $C1b$ structure is observed at a large scale with a very good chemical ordering in the unit cell. The magnetic properties have been investigated by x-ray magnetic circular dichroism and a superconducting quantum interferometer device and are compatible with the predicted half-metallic character. These NiMnSb layers have been integrated in single-crystalline NiMnSb/MgO/NiMnSb heterostructures for preparation of magnetic tunnel junctions with half-metallic electrodes.

Low-noise YBa2Cu3O7 rf SQUID magnetometer

A superconducting quantum interferometer device (SQUID) electronics with tank frequencies near 150 MHz was constructed to enhance the rf SQUID sensitivity. By these means we characterized our YBa2Cu3O7 thin-film rf SQUIDs with step-edge junctions immersed in liquid N2. We obtained transfer function values of over 40 μV/Φ0, at a 50 Ω input impedance, for both hysteretic and dispersive mode of rf SQUID operation. The rms white and 1/f flux noise levels were significantly lower than at the tank frequency of 20 MHz. The best magnetic field sensitivity at 77 K was 0.9 pT/Hz1/2, and the energy resolution 1.4×10−28 J/Hz, down to 0.3 Hz.