A magnetometer of weak quasi-stationary and high-frequency fields on resonator microstrip transducers with thin magnetic fields

A high-sensitivity magnetometer for simultaneous measurements of three components of a weak quasi-stationary or high-frequency magnetic-field vector was developed and investigated. Microstrip structures that are based on irregular resonators serve as the magnetometer transducers. An anisotropic thin-film magnetic structure is used as the sensing element. This structure consists of two thin magnetic films that are prepared by magnetron sputtering of a Ni₇₅Fe₂₅ permalloy target and separated by a silicon monoxide layer. It is demonstrated that the transducer exhibits the maximum sensitivity, when the easy magnetization axis of the film structure is orthogonal to the polarization direction of the pumping microwave magnetic field in the microstrip resonator and at an optimal value of a constant magnetic bias field and its optimal deflection from the pumping-field polarization direction which is parallel to it. The magnetometer is characterized by a wide dynamic range of measured magnetic fields, 10^–10–10^–4 Т, and a wide frequency range, 10^–1–10⁵ Hz.     

Measurements of strong pulsed magnetic fields by Hall effect devices

The possibility of using Hall effect devices for measuring strong pulsed magnetic fields is studied. The Hall effect devices with a∼10-mV/T sensitivity, based on 1- to 3-μm-thick n-type InAs polycrystalline films with a 10³-cm²/(Vs) electron mobility and ∼10¹⁸-cm-³ concentration, are used. It is established that the Hall effect voltage of these devices is a linear function of the field in magnetic fields with an induction of up to 56 T, and they are suitable for measuring unipolar strong pulsed magnetic fields at induction variation rates of up to ~10⁵T/s. It is necessary to use more sensitive Hall effect devices to obtain higher signal-to-noise ratios for rapidly measuring alternating fields.     

An automatic setup for measuring low-field temperature dependencies of magnetoresistances of film samples

A simple method for magnetoresistance measurements in weak fields based on using a low-frequency alternating magnetic field is proposed. The special feature of this method is the direct measurement of the difference in resistance ΔR of the sample under study in the field and in the absence of the field, which offers a chance to significantly increase measurement sensitivity. The automatic setup for measuring temperature dependencies of magnetoresistance of film metallic samples with a ΔR sensitivity of up to 10^?7 Ω is described. The temperature dependencies of magnetoresistance of thin-film nanocrystalline Co-Cu alloy samples in weak magnetic fields and in a temperature range of 77–300 K are studied.     

High-Sensitivity Magnetometers Based on HTSC Ceramics

The magnetic response of the YBa₂Cu₃O_{7 – x} superconducting ceramics to an alternating magnetic field was studied experimentally. A magnetometer with a sensitivity level of 2 × 10^–7Oe was developed on the basis of the experimental data. The ways of improving such devices are discussed.     

Determination of magnetic field using a Fabry–Perot cavity containing novel nanoparticles

Mn_0.75Zn_0.25Fe₂O₄ nanoparticles were used to characterize magnetic fields using an all-fiber Fabry–Perot interferometer. The 20-nm nanoparticles were fabricated with citrate and displayed a coercive field of approximately 10?mT. The nanoparticles were dispersed in oleic acid to prepare a magnetic fluid to fill a Fabry–Perot structure fabricated by arc splicing with conventional single-mode and hollow core photonic crystal fibers. This device provided sensitivity and resolution of 0.11?dB/mT and 0.09?mT, respectively. Thermal analysis indicated that the magnetic measurements are weakly depending on temperature (0.7?pm/°C and 7?×?10^?3?dB/°C). This device offers low-cost fabrication, simple implementation and may be used in several industrial applications.     

A high-sensitivity Hall magnetometer

Based on two Hall transducers, a low-frequency magnetometer with a sensitivity of 2.5 × 10^–3 G/Hz^1/2 is designed. The dynamic range of the magnetometer at a frequency of 19 Hz varies from 2.5 × 10^–3 to ±8 × 10⁴ G.     

A Torsion Balance for Studying Anisotropic Magnetic Properties of Superconducting Materials

A low-temperature torsion balance for studying magnetic properties of superconductors is described. The device can operate in the modes of the rotation or vibration of an axisymmetric superconducting sample in an external magnetic field. The balance provides for the measurement of a torque of 10^–8 –1 N·m applied to the sample. The device is highly sensitive to frozen magnetic fluxes even of the order of magnitude of the geomagnetic field (H 0.5 Oe). To eliminate the effect of frozen magnetic fluxes, two-layer Permalloy shields providing for the cooling of the sample in the field H < 10^–3 Oe are used. The capabilities of the developed method for studying critical parameters and the anisotropic magnetic properties of superconductors are described.     

Magnetic-field sensors based on lead-doped lanthanum manganites

The possibility of using lead-doped lanthanum manganites as materials for magnetically sensitive elements of sensors is considered. Measurements of the penetration coefficient of a radio-frequency electromagnetic field as a function of the strength of a stationary magnetic field have been performed. Two variants of using cores made from lanthanum manganites are analyzed. It is shown that cores made from lead-doped lanthanum manganites allow measurements of magnetic fields to be performed in the range 80?4 × 10⁶ A/m. A sensitivity of up to 2.5 × 10^?2%/A/m can be achieved for fields of 80?8 × 10³ A/m.     

Detection of Superconductivity in a High-Pressure Chamber with Diamond Anvils by Mutual Induction Method with Laser-Modulated Sample Temperature

An improved method for detecting the transition of a sample to the superconducting state at high pressure in a chamber with diamond anvils is proposed. The background signal and the signal determined by the transition of a sample to the superconducting state are separated using the method of a periodic destruction of the superconducting state, achieved by heating the sample with low-frequency modulated laser radiation. This method allows magnetic materials to be used in the manufacture of parts for the high-pressure chamber. The heat release in the cryostat, associated with the heating of the modulating inductance coil and the absorption of laser radiation, is no higher than a few milliwatts, thereby allowing the extension of the temperature range accessible to modulation methods for detecting superconductivity. Examples of applying this technique to the detection of superconducting transitions in Pb, V, and YBa₂Cu³O^{7 − x} samples are presented.__________Translated from Pribory i Tekhnika Eksperimenta, No. 4, 2005, pp. 137–143.Original Russian Text Copyright © 2005 by Timofeev, Utyuzh.     

Thermal imaging system based on a high-temperature superconductor

A laboratory prototype of an infrared imaging system is described. Its operating principle is based on the formation of an area on the surface of a patterned high-temperature superconducting (HTSC) film, which is sensitive to external radiation and its displacement by local heating. The basic parameters of the activated pixel zone were measured: dimensions A ≈ (95 × 95) μm², detectivity D* = 1.3 × 10⁸ cm Hz^1/2/W, and the time constant τ = 6 ms. The considered pixel-by-pixel data readout procedure and the bolometric nature of the detector sensitivity open the possibility of utilizing the imaging system over a broad spectral range.     

Constitutive modeling for Ti-6Al-4V alloy machining based on the SHPB tests and simulation

A constitutive model is critical for the prediction accuracy of a metal cutting simulation. The highest strain rate involved in the cutting process can be in the range of 10~4–10~6 s~(–1). Flow stresses at high strain rates are close to that of cutting are difficult to test via experiments. Split Hopkinson compression bar(SHPB) technology is used to study the deformation behavior of Ti-6Al-4V alloy at strain rates of 10~(–4)–10~4s~(–1). The Johnson Cook(JC) model was applied to characterize the flow stresses of the SHPB tests at various conditions. The parameters of the JC model are optimized by using a genetic algorithm technology. The JC plastic model and the energy density-based ductile failure criteria are adopted in the proposed SHPB finite element simulation model. The simulated flow stresses and the failure characteristics, such as the cracks along the adiabatic shear bands agree well with the experimental results. Afterwards, the SHPB simulation is used to simulate higher strain rate(approximately 3×10~4 s~(–1)) conditions by minimizing the size of the specimen. The JC model parameters covering higher strain rate conditions which are close to the deformation condition in cutting were calculated based on the flow stresses obtained by using the SHPB tests(10~(–4)–10~4 s~(–1)) and simulation(up to 3×10~4 s~(–1)). The cutting simulation using the constitutive parameters is validated by the measured forces and chip morphology. The constitutive model and parameters for high strain rate conditions that are identical to those of cutting were obtained based on the SHPB tests and simulation.     

FT-ICR mass spectrometry: Superconducting magnet,external ion source,ion–molecule reactions,and ion–ion traps

The world of Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry has witnessed, especially in the last 30 years significant advances in many fields of science, such as electronics, magnets, new ICR cell designs, developed ICR event sequences, modern external ionization sources, and linear ion beam guides, as well as modern vacuum technology. In this review, a brief account is given focusing especially on the studies performed in Wanczek's group and ICR research laboratory at the University of Bremen. An FT-ICR mass spectrometer has been developed with a high magnetic field superconducting magnet, operating at 4.7 T. At this magnetic field, a trapping time of 13.5 h was obtained with 30% efficiency. For the tetrachloromethane molecular ion, m/z 166, a mass-resolving power m/Δm = 1.5 × 10⁶ was measured at a pressure of 2 × 10⁻⁸ Torr. The transition from magnet sweep to frequency sweep and the application of Fourier-transform has greatly enhanced the ICR technology. External ion sources were invented and differential pumping schemes were developed for enabling ultrahigh vacuum condition for ICR detection, while guiding ions at relatively higher pressures, during their flight to the ICR cell. With the external ion source, a time-of-flight ICR tandem instrument is built. A method to measure the ion flight time and to trap the ions in the ICR cell is described. Many ICR cell characteristics such as z-axis ion ejection and coupling of radial and axial ion motions in a superposed homogeneous magnetic and inhomogeneous trapping electric field were extensively studied. Gas-phase ion–molecule reactions of several reactive inorganic compounds with a focus on phosphorous and sulfur as well as silicon chemistry were also studied in great detail. The gas-phase ion chemistry of several trifluoromethyl-reagents such as trifluoromethyltrimethylsilane and tris(trifluoromethyl)phosphine were also investigated in ICR. Dual polarities multisegmented ICR cells were invented and deeply characterized. Sophisticated ICR pulse event programs were developed to enable long-range ion–ion interactions between simultaneously trapped positive and negative ions.     

Wear of magnetic materials and audio heads sliding against magnetic tapes

The friction and wear of various materials and audio heads sliding against magnetic tapes were studied. Magnetic materials such as Permalloy, Sendust and hot-pressed ferrite (HPF) and some other non-magnetic materials were used as material specimens. Three types of audio heads for cassette tape recorders were used as the head specimens. Their magnetic cores were made from ordinary Permalloy, hard Permalloy and HPF. An experiment using a conical diamond slider was carried out to study the wear resistance of various materials. The specific wear rates of the various material specimens and components of the heads such as the core, shield plate and epoxy resin were measured using the Knoop indentation technique. Wear did not occur uniformly over the surfaces of the Permalloy heads. This irregular wear was examined in detail and its origin is discussed. The specific wear rates of Permalloy and HPF are of the order of 10^?5 mm³ N^?1 m^?1 and 10^?6 mm³ N^?1 m^?1 respectively and that of epoxy resin is of the order of 10^?4 – 10^?5 mm³ N^?1 m^?1. The coefficient of friction of an HPF head is about 0.3, while that of both types of Permalloy head is about 0.7. It is concluded that the mechanism of wear by magnetic tape is not entirely due to the abrasive action of the magnetic powder in the tape but is also partially adhesive in nature.     

Precision Measurements and Compensation for the Transverse Components of the Solenoids' Magnetic Field

A device developed at the Budker Institute of Nuclear Physics (BINP) to measure with a high precision the direction of the magnetic field lines in the vicinity of the solenoid axis is described. The transverse field components are automatically measured by a small (<15 cm³ in volume) compass-based sensor during its motion along the axis. The sensor's absolute sensitivity is ～0.1–0.9 mG and is limited only by external vibration noise. The upper bound of this range (～1 G) is governed by the current in the circuits producing the fields that compensate for the local misalignments of the field lines. The capabilities of the device are illustrated by the results from adjusting the solenoid fields in electron coolers recently built by the BINP. The procedures used to do this are described. The feasibility of obtaining the highest-quality field is shown. For one plant with a field intensity of ～1 kG, the rms deviation of the field lines from the axis is <10^?5 rad within a length of 3 m.     

Uncertainty evaluation of a 10N·m dead weight torque standard machine and comparison with a 1kN·m dead weight torque standard machine

A 10N·m dead weight torque standard machine (10-N·m-DWTSM) has been developed and evaluated since 2006 at the National Metrology Institute of Japan (NMIJ), a part of the National Institute of Advanced Industrial Science and Technology (AIST). Previously, the lengths of a moment arm, made of a low-thermal-expansion alloy (Super Invar), and the sensitivity limit of the fulcrum were evaluated. However, it is known that mechanical parts made of Super Invar vary in size with time. Therefore, the sensitivity limit of the fulcrum should be investigated under real calibration conditions. In this study, the moment arm lengths and the sensitivity limit of the fulcrum were re-evaluated. The moment arm lengths were found to have increased by an average of 6.3 μm in five years. The relative combined standard uncertainty of the moment arm length, w_arm, was re-evaluated in consideration of the uncertainty of the secular length change and was found to be 1.8 × 10⁻⁵. The sensitivity limit of the fulcrum was investigated by using a highly accurate, small-rated-capacity torque measuring device. The relative combined standard uncertainty due to the sensitivity limit of the fulcrum was 2.5 × 10⁻⁵ in the 0.1–10N·m torque range. The uncertainty budget table of the 10-N·m-DWTSM was completed. The relative expanded uncertainty of torque realized by the 10-N·m-DWTSM, W_tsm, was evaluated in the 0.1–10N·m torque range and was found to be 6.6 × 10⁻⁵, with a coverage factor, k, being equal to 2. In addition, the 10-N·m-DWTSM was compared with the existing 1-kN·m-DWTSM at NMIJ by using small-rated-capacity torque measuring devices at 5N·m and 10N·m torque steps. Two loading conditions were adopted in this comparison. The comparison results showed good agreement within the uncertainties in all cases. Thus, the torque realized by the 10-N·m-DWTSM was shown to be equivalent to that achieved by the 1-kN·m-DWTSM.     

Highly sensitive curvature sensor based on an asymmetrical Mach–Zehnder interferometer

Mach–Zehnder interferometers have attracted attention due to their flexible structures and extensive applications. In this study, a simple and highly sensitive curvature sensor based on an asymmetrical Mach–Zehnder interferometer comprising an up-taper and a peanut-like section was theoretically and experimentally characterized. A simulation was conducted to investigate the influence of structural parameters on the interference spectrum. Experimental measurements show that a high curvature sensitivity of ?35.3?nm/m^?1 from 1.35 to 2.20?m^?1 was obtained and high mechanical strength was demonstrated. The temperature–curvature cross-sensitivity of 4.44?×?10^?4?m^?1/°C was lower than the curvature resolution. The high curvature sensitivity and low temperature cross-sensitivity make this sensor a candidate for practical applications.     

A three-axes-compensated inductive magnetometer for measurements in high pulsed magnetic fields

A high-sensititity magnetometer intended for studying the magnetic properties of materials in pulsed magnetic fields of up to 43 T is described. A distinctive feature of the magnetometer is its method for compensating pickups generated in the magnetometer sensing element by a pulsed field. The commonly used uniaxial high-order compensation is replaced by a triaxial compensation of the lowest (quadrupole) order, combined with a transverse arrangement of the main probe coils. This method has allowed us to achieve a compensation level of the signal in the working coil (with an inner diameter of 1.4 or 1.75 mm) of the magnetometer without a sample of up to 10⁻⁶ for the longitudinal and 10⁻⁴ for the transverse field components. The magnetic moment sensitivity of the magnetometer is 10⁻⁴ mA·m² in fields below 10 T and 10⁻³ mA·m² at a field pulse amplitude of 35 T. A deviation of the compensation is below 2×10⁻⁴ for a temperature increase from 77 to 300 K and below 5×10⁻⁵ after sample replacement. The sample temperature is controlled by a fast-acting temperature control system in a range of 6–300 K to an accuracy of 0.3–0.05 K.     

The μSR setup on the muon beam of the synchrocyclotron at the Konstantinov Institute of Nuclear Physics

The μSR setup for investigating the distribution of magnetic fields in solids using the muon spin rotation (μSR) method is described. The setup is characterized by a high degree of homogeneity of the magnetic field at the site of the sample under investigation, compensation of scattered magnetic fields to a level of ?10^?2 G, and a time resolution of 2.5 ns (the full width at half-maximum). The setup is suitable for μSR measurements on samples in the temperature range of 5–300 K with a precision of ±0.1 K.     

Ft-Icr Studies With Laser-Generated Supersonic Cluster Beams

ABSTRACT

By using a combination of einzel lenses and deceleration grids, it is possible to inject cold molecular ions from a supersonic beam apparatus directly into the superconducting magnetic trap of a Fourier Transform Ion Cyclotron Resonance (FT-ICR) spectrometer^1,2. The injection cycle may be repeated many times until the trap is “filled” with an adequate number of ions. Since the ion source is completely independent of the FT-ICR apparatus, and since the injection is mass-specific and nearly 100% efficient, these techniques may find wide application in the analysis and study of complicated molecules and clusters. Examples are given for the application of this new technique to the study of dissociative chemisorption on the surface of metal and semiconductor clusters, and to the study of the “soccerball” molecule, C₆₀ ⁺, and its metal-substituted complex, C₆₀La⁺.     

A highly sensitive field mill for registering weak and strong variations of the electric-field intensity of the Earth’s atmosphere

The design and the principle of operation of an electric-field intensity meter (field mill) are described. The instrument is intended for determining the energy, time, and spatial parameters of the atmospheric electric field near the Earth’s surface when monitoring a geophysical situation. The developed field mill allows registering both weak variations of the electric-field intensity in the atmosphere, such as global electromagnetic Schumann resonances, and strong variations that are caused by the passage of atmospheric fronts, heavy clouds, thunderstorms, etc. The instrument has a threshold sensitivity of ~10^–3 V/(m Hz^1/2) within a frequency range of 10^–3–25 Hz and a wide dynamic range of 120 dB.