Superconducting Quantum Interference Device Magnetometry Research Articles

Synthesis and characterization of single-crystalline nanowires of bismuth doped with manganese

We report the first synthesis of nanowires of bismuth doped with manganese prepared via an homogeneous non-aqueous solution reaction. By studying intermediates at different temperatures during the nanowire growth process, the evolution of the crystallization of metallic products and the mechanism of nanowire formation are investigated. In this work, a combination of TEM (transmission electron microscopy), XRD (X-ray powder diffractometry), ICP (inductively-coupled plasma spectrometer) and SQUID (superconducting quantum interference device) magnetometry were employed to characterize the morphology, structure, composition and magnetic properties of the products.

The synthesis of core–shell iron@gold nanoparticles and their characterization

Au-coated magnetic Fe nanoparticles have been successfully synthesized by partial replacement reaction in a polar aprotic solvent with about 11 nm core of Fe and about 2.5 nm shell of Au. In this work, a combination of TEM (transmission electron microscopy), XRD (X-ray powder diffractometry), EDS (energy disperse X-ray spectroscopy), SQUID (superconducting quantum interference device), TGA (thermograviometric analysis) and UV–visible absorption spectroscopy were employed to characterize the morphology, structure, composition and magnetic properties of the products. HRTEM images show clear core–shell structure with different crystal lattices from Fe and Au. SQUID magnetometry reveals that particle magnetic properties are not significantly affected by the overlayer of a moderately thick Au shell. The Au-coated particles exhibit a surface plasmon resonance peak that red-shifts from 520 to 680 nm. And all the above characterizations show that in this sample there are no iron oxides inside the particle.

Design for a multifrequency high magnetic field superconducting quantum interference device-detected quantitative electron paramagnetic resonance probe: Spin-lattice relaxation of cupric sulfate pentahydrate (CuSO4⋅5H2O)

We have designed a spectrometer for the quantitative determination of electron paramagnetic resonance (EPR) at high magnetic fields and frequencies. It uses a superconducting quantum interference device (SQUID) for measuring the magnetic moment as a function of the applied magnetic field and microwave frequency. We used powdered 2,2-diphenyl-1-picrylhydrazyl to demonstrate resolution of g-tensor anisotropy to 1 mT in a magnetic field of 3 T with a sensitivity of 1014 spins per 0.1 mT. We demonstrate multifrequency operation at 95 and 141 GHz. By use of an aligned single crystal of cupric sulfate pentahydrate (chalcanthite) CuSO4⋅5H2O, we show that the spectrometer is capable of EPR line shape analysis from 4 to 200 K with a satisfactory fit to a Lorentzian line shape at 100 K. Below 100 K, we observed line-broadening, g shifts, and spectral splittings, all consistent with a known low-dimensional phase transition. Using SQUID magnetometry and a superconducting magnet, we improve by an order of magnitude the sensitivity and magnetic field range of earlier power saturation studies of CuSO4⋅5H2O. We were able to saturate up to 70% of the magnetic moment with power transfer saturation studies at 95 GHz, 3.3 T, and 4 K and obtained the spin-lattice relaxation time, T1=1.8 ms, of CuSO4⋅5H2O at 3.3 T and 4 K. We found an inverse linear dependence of T1, in units of seconds (s) at 3.3 T between 4 and 2.3 K, such that T1=0.016⋅K⋅s⋅τ−1−0.0022⋅s, where τ is the absolute bath temperature. The quantitative determination of EPR is difficult with standard EPR techniques, especially at high frequencies or fields. Therefore this technique is of considerable value.

Remote detection of corrosion activity by SQUID magnetometry across a multiphase medium under electrolyte flow conditions

Hydrodynamic induction of magnetic fields on AA2024 sample corroding in NaOH solutions was studied by a Superconducting Quantum Interference Device (SQUID) magnetometer operating in liquid helium with a spatial resolution of approximately 1 mm. The hydrodynamic generation of magnetic fields was explained in terms of electronic and ionic currents induced by corrosion potential gradients within the sample due to different solution flow velocities. The intrinsic magnetic activity of the electrolyte flow was significantly less than that of the corroding sample. The measurements demonstrated a unique capability of magnetometry to sense corrosion remotely and across the integrated media consisting of gaseous and solid dielectrics (air, plastics), electronic conductor (aluminum alloy) and ionic one (solution).

Structure and Magnetic Switching of Thin-Film a-HITPERM/<tex>$hboxSiO_2$</tex>Soft Magnetic Multilayers

Laminated (Fe/sub 0.7/Co/sub 0.3/)/sub 88/Zr/sub 7/B/sub 4/Cu/sub 1/ amorphous HITPERM/SiO/sub 2/ multilayer thin films have been studied by room-temperature (RT) pulsed inductive microwave magnetometry (PIMM) in single, bilayer, and trilayer films. Switching has been measured in a multilayer film with six (50 nm) HITPERM layers, separated by five (2 nm) SiO/sub 2/ layers. Films were investigated by conventional transmission electron microscopy (TEM), high-resolution TEM (HREM), and superconducting quantum interference device (SQUID) magnetometry. HREM and TEM show BCC FeCo nanocrystals to nucleate on top of SiO/sub 2/ layers. Plan view TEM on the top layer reveals FCC nanocrystals that align in chains with spacing of /spl sim/50-100 nm. SQUID magnetometry shows reversal to begin by rotation in a single layer for H<14.4 kA/m (180 Oe) followed by nearly simultaneous reversal of several layers. A final switching event is thermally activated, requiring fields in excess of 8 kA/m (100 Oe) to switch at 2 K, but switching at the same field as other layers for elevated temperatures (RT).

Possible Pitfalls in SQUID Magnetometry of Superconducting Samples: The Case of RuSr2GdCu2O8

Inhomogeneities of the field in the superconducting magnet of a superconducting quantum interference device (SQUID) magnetometer can create serious artefacts in the d.c. magnetization measurements of superconducting samples. We discuss the problem focusing on the procedure of calculating the magnetic moment of a sample from the measured SQUID output signal. The (weakly) ferromagnetic superconductor RuSr2GdCu2O8 has been reported sensitive to inhomogeneities of the SQUID's superconducting magnet, which create artefacts in its measured magnetization. Indeed, we show that, because of the small values of the magnetic hysteresis width, field changes less than 100 μT over the scanning length inside the magnet are enough to create spurious signals in the measured magnetic moment of this compound.

SuperconductingRuSr2GdCu2O8studied by SQUID magnetometry

For polycrystalline ${\mathrm{RuSr}}_{2}{\mathrm{GdCu}}_{2}{\mathrm{O}}_{8}$ (Ru-1212), distinct peaks have been reported in dc magnetization in the superconducting state of the sample. ${\mathrm{Sr}}_{2}{\mathrm{GdRuO}}_{6}$ (Sr-2116), the precursor for the preparation of Ru-1212, shows similar peaks in the same temperature regime. Based on measurements performed on both bulk and powdered samples of Ru-1212 and Sr-2116, we exclude the possibility that the observed behavior of the magnetization of Ru-1212 is due to Sr-2116 impurities. The effect is related to the superconductivity of Ru-1212, but it is not an intrinsic property of this compound. We provide evidence that the observation of magnetization peaks in the superconducting state of Ru-1212 is due to flux motion generated by the movement of the sample in an inhomogeneous field, during the measurement in the superconducting quantum interference device (SQUID) magnetometer. We propose several tests that help to decide whether the features observed in a SQUID magnetization measurement of Ru-1212 represent a property of the compound or not.

Mineralogy of a natural As-rich hydrous ferric oxide coprecipitate formed by mixing of hydrothermal fluid and seawater: Implications regarding surface complexation and color banding in ferrihydrite deposits

We characterized the most As-rich natural hydrous ferric oxide (HFO) material ever reported using powder X-ray diffraction (pXRD), transmission electron microscopy (TEM), X-ray fluorescence spectroscopy (XRF), light element analysis using gas chromatography (GC), visible-infrared (vis-IR) diffuse reflectivity, 57 Fe Mössbauer spectroscopy, and superconducting quantum interference device (SQUID) magnetometry. We find that the natural As-HFO material is very similar to synthetic coprecipitated As-HFO materials, but is significantly different from all known natural and synthetic As-free HFO materials and ferrihydrite samples. The pXRD patterns show systematic differences with patterns for 2-line ferrihydrite, that are interpreted as evidence for significant populations of oxygen-coordinated Fe-As pairs. Observations by TEM, combined with energy dispersive spectroscopy (EDS) microanalysis, show agglomerations of nanophase primary particles and no evidence for other Fe- or As-bearing phases. Mössbauer spectroscopy shows octahedrally coordinated Fe 3+ , with a large fraction (~20%) of the octahedral Fe environments that are significantly distorted by the presence of As, compared to the Fe local environments in As-free ferrihydrite and HFO samples. The loss on ignition (LOI) is quantitatively consistent with OH + H 2 O, measured by GC, which, in turn, is consistent with ~1 nm diameter primary particles having all their surface cations (Fe 3+ , As 5+ , Si 4+ , C 4+ ) coordinated on the free surface side by OH - and OH 2 . The banding into adjacent yellowish and reddish layers that occurs in the As-HFO deposits was studied by performing mineralogical analyses of the separated adjacent layers of two couplets of yellowish and reddish material. The yellowish samples were found not to contain secondary crystalline phases (as did the reddish samples, in small amounts) and to be relatively As-rich, C- and Si-poor. The observed anticorrelations between As and Si and between As and inorganic C suggest that natural HFOs, which usually contain significant molar amounts of Si, may not be as efficient at surface complexing As (and P) as their Si and C-free synthetic counterparts, unless formed by co-precipitation with the As (or P). The yellowish and reddish layers were also clearly resolved by both Mössbauer spectroscopy and magnetometry. Complexation of arsenate onto the HFO core was found to significantly increase the average quadrupole splitting (QS) obtained from Mössbauer spectroscopy by an amount that could not be explained by other chemical differences and that is consistent with an ~1 nm diameter particle size and somewhat smaller HFO core. The Munsell hue YR index (5-10 YR) was found to be strongly correlated to the average QS, thereby establishing that the color differences, corresponding to the measured shifts of the main visible band edge, are due to the local distortions in the [6]Fe3+ environments that are induced by As complexation, via their influence on the relevant ligand field transitions. SQUID magnetometry allows the following observations. (1) The superparamagnetic to superferromagnetic transitions occur at 25 K and lower in As-HFO, compared to 55 K in synthetic 2-line ferrihydrite, suggesting a smaller magnetic primary particle (or core) size for As-HFO and inter-particle magnetic interaction reduction by surface complexed As, Si, and C. (2) The ratio of supermoment magnitude to magnetic particle size (m 2 /n, where m is the net number of Fe 3+ atomic moments per supermoment and n is the number of Fe 3+ cations per particle or HFO core) decreases with increasing As content in the sequence synthetic-HFO &gt; reddish-As-HFO &gt; yellowish-As-HFO. (3) The magnetic susceptibility magnitudes for As-HFO and synthetic 2-line ferrihydrite differ by a factor of 10 and suggest different supermoment formation mechanisms (m 2 /n &lt; 1 vs. m 2 /n &gt; 1, respectively) related to differences in intra-particle cationic and anionic disorder and magnetic particle size.

Interband Faraday and Kerr rotation and magnetization ofPb1−xEuxTein the concentration range 0&lt;x⩽1

Faraday and magneto-optical Kerr effect has been used for the investigation of the band alignment as well as of the magnetic properties of epitaxial layers of the ternary alloy system ${\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Eu}}_{x}\mathrm{Te}$ $(0&lt;~x&lt;~1)$ grown on ${\mathrm{BaF}}_{2}$ substrates. Due to the wide range of transition energies $(0.19\mathrm{eV}&lt;~{E}_{g}&lt;~2.25\mathrm{eV})$ the experiments had to be performed in the spectral range from midinfrared to visible light. Data were collected at temperatures between 1.8 and 250 K and in magnetic fields up to 7 T. Concomitant magnetization measurements $(B=1\mathrm{T})$ were performed with a superconducting quantum interference device (SQUID) magnetometer and compared with measurements of the x dependence of the Verdet constant. The variation of the fundamental absorption gap with Eu content can be understood in terms of the relative energetic position of PbTe-related band edges and $\mathrm{Eu}4f$ and $5d$ levels: $\ensuremath{\Delta}{E}_{g}/\ensuremath{\Delta}x=4.48\mathrm{eV}$ for $x&lt;0.06;$ $\ensuremath{\Delta}{E}_{g}/\ensuremath{\Delta}x=2.03\mathrm{eV}$ for $0.06&lt;x&lt;0.6.$ For $x&gt;0.8,$ the electronic transitions are identified to be EuTe-like. The most striking feature is a sign reversal of Verdet's constant around $x=0.15,$ which is attributed to a crossover of Faraday rotation caused by band electrons (holes) and interacting pairs of magnetic ions and a metal-insulator transition. An antiferromagnetic phase transition is observed for $x&gt;0.8$ in magneto-optics as well as in SQUID magnetometry.

Design of a NDE instrumentation prototype with high-temperature SQUIDs

Eddy currents non-destructive evaluation (NDE) consists in the use of electromagnetic techniques through which the inspection is carried out by detecting magnetic anomalies in the material under examination. The exploitation of the very high sensitivity of SQUID superconducting magnetometers to magnetic flux variations makes it an interesting and promising candidate for magnetic field detection. SQUID (superconducting quantum interference device) magnetometry can allow to overcome the traditional limits due to the lack of sensitivity in conventional electromagnetic NDE techniques. In this paper we present a new project concerning the design of a prototype of a high-temperature SQUID-based NDE instrumentation and its mains applications.

Detection of Parasites in Fish by Superconducting Quantum Interference Device Magnetometry

ABSTRACTCandling, the traditional means of detecting parasites during fish fillet processing, is time consuming and labor intensive. This method is a major factor in reducing the quality and increasing the cost of fish brought to market. The difference in electrical conductivity between fish and an embedded parasite was hypothesized to be a practical basis for an instrument which would have potential for automated parasite detection. A small electrical current was passed through a parasite‐containing fillet and the magnetic field above the fillet was recorded by a Superconducting Quantum Interference Device magnetometer. Results indicate potentially successful detection of parasites by the device.

Crystallographic and magnetic properties of CoxFe1−xCr2S4

The mixed series CoxFe1−xCr2S4 has been studied by x-ray, Mössbauer spectroscopy, and superconducting quantum-interference device (SQUID) magnetometry. The crystal structure is found to be a cubic spinel, and the lattice constant a0 decreases linearly with increasing cobalt concentration. Mössbauer spectra of CoxFe1−xCr2S4 have been taken at various temperatures ranging from 4.2 to 300 K. The iron ions are ferrous and occupy the tetrahedral sites. The Curie temperature increases linearly with cobalt concentration, suggesting that the superexchange interaction for the Co-S-Cr link is stronger than that for the Fe-S-Cr link. Magnetic hyperfine and quadrupole interactions in Co0.9Fe0.1Cr2S4 at 4.2 K have been studied, yielding the following results: Hhf=80.8 kOe, 1/2e2qQ(1+1/3η2)1/2=2.65 mm/s, θ=15°, φ=75°, and η=1.0. It is notable that, as the temperature decreases below the Curie temperature, quadrupole splitting increases with decreasing temperature, suggesting the presence of an electric field gradient and accompanying relaxation effects. Magnetic susceptibility measurements by SQUID magnetometry show that superexchange interactions between Fe2+ ions are ferrimagnetic.

Magnetic properties of the monoclinic FeRh2Se4

FeRh2Se4 has been studied by x-rays, Mössbauer spectroscopy, and superconducting quantum interference device (SQUID) magnetometry. Mössbauer spectra of FeRh2Se4 have been taken at various temperatures ranging from 4.2 to 550 K. Magnetic hyperfine and quadrupole interactions at 4.2 K have been fitted, yielding the following results: H=161.6 kOe, 1/2e2qQ(1+1/3η2)1/2=−0.93 mm/s, θ=61°, φ=0°, and η=0.1. The temperature dependence of the quadrupole splitting, calculated in terms of direct lattice-sum calculations using x-ray crystallographic data, is in good agreement with experimental values up to 550 K. The axial field parameter Δ1=2.0‖λ‖, the rhombic field parameter Δ2=3.3‖λ‖, and the covalency factor α2=0.65 were obtained. Magnetic susceptibility measurements by dc SQUID magnetometry show that superexchange interactions between Fe2+ ions are antiferromagnetic.

Kinetics of orientation of a side‐chain liquid–crystal polymer as measured by a high‐temperature SQUID‐magnetometer

AbstractA superconducting quantum interference device (SQUID) magnetometer suitable for measurements of the magnetic susceptibility up to 600 K has been used to follow the kinetics of realignment in the nematic phase of a side‐chain liquid–crystal polymer. Experiments are performed using monodomain and polydomain samples. Results obtained in monodomain samples are in quantitative agreement with the prediction of the continuum theory up to an angle of approximately 60°. Experiments conducted at higher starting angles give clear indication of backflow effects. Data obtained from experiments on polydomain samples have been compared with model calculations using the data on the monodomain samples. This comparison leads to the conclusion that in this case backflow effects play an important role, too. All results show that SQUID magnetometry allows monitoring of the kinetics of realignment with highest precision. © 1992 John Wiley &amp; Sons, Inc.

The fabrication and characterization of high temperature superconducting magnetic shields

Tubes fabricated of polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-x/ are characterized, and details of the fabrication procedure are discussed. The microstructure of the tubes determined by scanning electron microscopy and X-ray diffractometry is described. Resistive measurements of T/sub c/ and Delta T/sub c/ have been made. The tubes have also been characterized by means of SQUID (superconducting quantum interference device) magnetometry. The temperature dependence of magnetic fields trapped axially in the tubes has been measured and estimates of penetration depth are given. Moreover, measurements of the transverse shielding effectiveness of the tubes have been made and are compared with theoretical predictions. Studies on flux penetration into the tubes are described. Findings from the microstructure studies are correlated with the observed superconductivity properties. The results on the high-temperature materials are compared to results obtained previously on tubes made from conventional superconductors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Rapid methods for the calculation of the magnetic fields associated with the human thorax

Rapid calculation of magnetic fields close to a magnetized human thorax is investigated. The work has relevance to the potential use of SQUID (superconducting quantum interference device) magnetometry as a clinical diagnostic tool. The calculational method is based on a model of the human thorax which consists of 26 planes of 33*35 1-cm cubes, each of which has a magnetic susceptibility assigned on the basis of its biological content. The use of a reciprocity technique to calculate fields close to a thorax using this model has led to simplification of the computational problem to one of a series of multiplicative manipulations using a set of lookup tables. It is established that the reciprocity method is inherently more accurate and computationally faster than direct integral methods and shows relatively greater sensitivity to the internal structure of the thorax. >

Mossbauer and magnetization studies of amorphous NdFeB compositionally modulated thin films

Several NdFeB compositionally modulated thin films are studied by using both conversion electron Mossbauer spectra and SQUID (superconducting quantum-interference-device) magnetometry. Both the hyperfine fields and the easy magnetization magnitude are not correlated with the modulation characteristic length ( lambda ) while the magnetization perpendicular to the thin-film plane decreases as lambda increases. The spectra were recorded at room temperature being the gamma rays perpendicular to the substrate plane. The magnetization measurements were recorded by using a SHE SQUID magnetometer in applied magnetic fields up to 5.5 T and in the temperature range between 1.8 and 30 K.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Magnetic relaxation in Fe-(SiO2) granular films.

Magnetic relaxation of granular Fe-(${\mathrm{SiO}}_{2}$) solids with low metal-volume fraction has been studied by employing dc SQUID (superconducting quantum interference device) magnetometry and M\ossbauer spectroscopy with the characteristic measuring time differing by nine orders of magnitude. The blocking temperatures (${T}_{B}$), extrapolated to zero external field as measured by the two techniques maintain a constant ratio of 0.35 independent of samples. Arrhenius law was found adequate in describing the relaxation process, with a well-defined relaxation-time constant of ${\ensuremath{\tau}}_{0}$\ensuremath{\simeq}${10}^{\mathrm{\ensuremath{-}}13}$ sec. A cusp in the susceptibility is observed at ${T}_{B}$, below which irreversible difference between the field-cooled and zero-field-cooled magnetizations occurs. Despite this spin-glass-like behavior, granular magnetic systems are found to be fundamentally different from spin glasses.