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  • 1
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have developed a high-resolution ac susceptometer that uses a rf superconducting quantum interference device to directly measure the flux coupled into a superconducting detection coil from a sample's changing magnetic moment in an applied ac field. The system operates in a frequency range from 0.01 to 1500 Hz and an applied ac field range of 0.1–400 μT with a sensitivity of about 5×10−12 A m2 for magnetic moment measurement, and at a reduced sensitivity down to 0.001 Hz. The instrument is based on an existing dc magnetometer system and uses that system's temperature control and dc superconducting magnet to allow operation over a temperature range from 2 to 400 K and in applied dc fields of ±5.0 T. During a measurement all operations are controlled automatically by computer from a menu-driven software system, with user input required only on initiation of a measurement sequence. Both real and imaginary components of the ac susceptibility can be determined.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have recently developed a high-resolution magnetic imaging system based on an array of five superconducting pickup coils located within 1 mm of room temperature. The pickup coils are 1.70 mm in diameter and spaced 2.5 mm apart allowing spatial resolution of order 1 mm. They are each connected to an rf SQUID and have a magnetic field sensitivity of 3 pT/(square root of)Hz. The system includes a three axis nonmagnetic translation table for mounting the sample, a stage for temperature control, and complete computer control of all functions.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: New measurements of the static magnetization of 3He-B in contact with a variety of wall configurations are presented and compared with previous measurements in both A and B phases. At high pressure the data tend toward agreement with resonant-magnetism experiments, while near the polycritical point a large discrepancy between the results of the two methods remains.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The results of a number of experiments on the dynamic and static magnetic properties of superfluids3He-A and3He-B are presented as well as a description of the 160-MHz rf-biased SQUID system used to make the magnetic flux measurements. Properties of both A and B phases were studied in both a rectangular cavity, a quasiideal geometry for3He-A, and in a stack of parallel plates, a quasiideal geometry for3He-B. The following results are presented: (1) Systematic studies of the properties of the “wall-pinned” magnetization ringing mode in3He-B, including the zero time frequency, which shows a discrepancy with theory, and the relaxation, which tends to confirm the essence of the theoretical ideas; also included are a variety of data on the effect of the finite size of the magnetic field change and the “biasing” field. (2) A complicated propagating magnetic disturbance has been observed using a novel method and systematics of its properties are studied. (3) The linear ringing frequencies of the B and A phases at a pressure of 27.0 bar in the parallel plate geometry have been studied with a result consistent with the assignment of the ABM state to3He-A and the BW state to3He-B. (4) Nonlinear ringing has been studied in both A and B phases in both geometries for both the oscillatory and driven modes. In the limit 1-T/T c → 0 we find 2πf R /γΔH → 2 for both phases in both geometries. Although the general character of ringing frequencyf R as a function ofΔH follows the theory, there are substantial quantitative discrepancies which cannot be explained by relaxation. Relaxation has been observed and our results have been discussed by Ambegaokar and Levy. (5) New measurements of static magnetism in the parallel plate geometry show agreement with all earlier work, indicating that the discrepancy between static and dynamic measurements cannot be explained by a geometrical effect. An experimental manifestation of the AB interfacial energy enabled an estimate of the coherence length to be made which is in qualitative agreement with theory.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Longitudinal magnetic relaxation in both 3He-A and 3He-B is studied in a variety of magnetic fields and three different geometries. Relaxation as described by Leggett and Takagi is observed for particular geometries in both 3He-A and 3He-B within a very limited range of magnetic field and temperature near T c. Under certain other conditions the longitudinal magnetization in 3He-A does not relax monotonically in time. Relaxation in 3He-B very near the critical temperature is shown to be remarkably different following nominal 90
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this article, we describe an ultrahigh vacuum (UHV) compatible superconducting quantum interference device (SQUID) magnetometer system for investigations of surface, interface, and thin film magnetism. This system provides a new capability for a commercial SQUID magnetometer to characterize freshly deposited thin film samples transported from a separate molecular-beam epitaxy deposition facility without breaking vacuum. Magnetic measurements can be performed over a wide range of temperatures down to 4.2 K in applied magnetic fields as high as 1 T, and under a variable vacuum environment in which pressures as low as 10−10 Torr can be achieved. The combination of the extremely high sensitivity of the SQUID for magnetic measurements with UHV analysis techniques offers the unique capability for films to be prepared, processed, and characterized repeatedly without substantial contamination. The capabilities of the UHV-SQUID magnetometer system are demonstrated by in situ measurements of the magnetic properties of Co/CoO bilayered thin films grown on Si(100) single-crystal substrates by electron-beam evaporation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Exchange coupling between Co and Co-oxide in bilayer and trilayer thin-film structures has been studied using a recently developed ultrahigh vacuum SQUID magnetometer (UHVSQM) system. Using this novel technique, newly deposited Co films from a separate molecular beam epitaxy facility were transported into the UHVSQM without breaking vacuum and magnetically characterized before and after in situ room temperature oxidation. Field-cooled hysteresis measurements performed at low temperatures indicate the presence of a complex antiferromagnetic Co-oxide domain structure as a result of oxidation. The stability of the magnetic structure is determined by competition between frustration generated at the interface when the ferromagnetic Co moments are reversed and stabilizing antiferromagnetic anisotropy which becomes large only at low temperatures (〈150 K). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Publication Date: 2018-06-16
    Description: Ross E. Sager and Jung-Youn Lee Plasmodesmata are cytoplasmic communication channels that are vital for the physiology and development of all plants. They facilitate the intercellular movement of various cargos – ranging from small molecules, such as sugars, ions and other essential nutrients and chemicals, to large complex molecules, such as proteins and different types of RNA species – by bridging neighboring cells across their cell walls. Structurally, an individual channel consists of the cytoplasmic sleeve that is formed between the endoplasmic reticulum and the plasma membrane leaflets. Plasmodesmata are highly versatile channels; they vary in number and structure, and undergo constant adjustments to their permeability in response to many internal and external cues. In this Cell Science at a Glance article and accompanying poster, we provide an overview of plasmodesmata form and function, with highlights on their development and variation, associated components and mobile factors. In addition, we present methodologies that are currently used to study plasmodesmata-mediated intercellular communication.
    Print ISSN: 0021-9533
    Electronic ISSN: 1477-9137
    Topics: Biology , Medicine
    Published by Company of Biologists
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