Design and implementation of a scanning SQUID microscope

Vu, Lan; Harlingen, D. J. Van

doi:10.1109/77.233586

Cited by 69 publications

(29 citation statements)

References 7 publications

(2 reference statements)

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“…18,19,20,21 The SQUID microscope images shown here were made at a temperature of T < 5K, with the sample cooled and imaged in the same fields. The size of the pickup loop used will be indicated for each image.…”

Section: Experimental Methodsmentioning

confidence: 99%

Antiferromagnetic ordering in arrays of superconductingπ-rings

et al. 2005

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We report experiments in which one dimensional (1D) and two dimensional (2D) arrays of YBa2Cu3O 7−δ -Nb π-rings are cooled through the superconducting transition temperature of the Nb in various magnetic fields. These π-rings have degenerate ground states with either clockwise or counter-clockwise spontaneous circulating supercurrents. The final flux state of each ring in the arrays was determined using scanning SQUID microscopy. In the 1D arrays, fabricated as a single junction with facets alternating between alignment parallel to a [100] axis of the YBCO and rotated 90 o to that axis, half-fluxon Josephson vortices order strongly into an arrangement with alternating signs of their magnetic flux. We demonstrate that this ordering is driven by phase coupling and model the cooling process with a numerical solution of the Sine-Gordon equation. The 2D ring arrays couple to each other through the magnetic flux generated by the spontaneous supercurrents. Using π-rings for the 2D flux coupling experiments eliminates one source of disorder seen in similar experiments using conventional superconducting rings, since π-rings have doubly degenerate ground states in the absence of an applied field. Although anti-ferromagnetic ordering occurs, with larger negative bond orders than previously reported for arrays of conventional rings, long-range order is never observed, even in geometries without geometric frustration. This may be due to dynamical effects. Monte-Carlo simulations of the 2D array cooling process are presented and compared with experiment.

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Section: Experimental Methodsmentioning

confidence: 99%

Antiferromagnetic ordering in arrays of superconductingπ-rings

et al. 2005

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“…There are several different approaches to design a scanning SQUID microscope. Vu and van Harlingen [2], Kirtley et al [3], and Morooka et al [4] use a SQUID made from niobium. In their microscopes, the SQUID and the sample are at 4.2 K, and the stand-off distance between SQUID and sample is on the order of 10 µm [3].…”

Section: Scanning Squid Microscopes: Basic Principlementioning

confidence: 99%

“…With their system they could detect tantalum inclusions having a volume of as small as 10 -12 m 3 in a test sample made from high-purity niobium. The time needed to test a 30×30 cm 2 sheet was about 15 minutes and was thus short enough to test a large number of sheets in an acceptable time. As for proposed accelerator projects, such as TESLA [34], about 400,000 niobium sheets will have to be tested, the measuring speed of the NDE system used must be as high as possible.…”

Section: An Example Of a Squid-based Eddy Current Nde Systemmentioning

confidence: 99%

SQUIDs: microscopes and nondestructive evaluation

Mück

2005

phys. stat. sol. (c)

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PACS 85.25.Dq, 85.25.Hv SQUIDs (Superconducting Quantum Interference Devices) are magnetic field sensores with unsurpassed sensitivity. They are amazingly versatile, being able to measure all physical quantities which can be converted to magnetic flux. They are routinely fabricated in thin film technology from two classes of superconducting materials: high-temperature superconductors (HTS) which are usually cooled to 77 K, and low-temperature superconductors (LTS), which have to be cooled to 4.2 K. SQUIDs have many applications, two of which shall be discussed in this paper. In SQUID microscopy, a SQUID scans a sample, which preferrably is at room temperature, and measures the two-dimensional magnetic field distribution at the surface of the sample. In order to achieve a relatively high spatial resolution, the stand-off distance between the sample and the SQUID is made as small as possible. SQUIDs show also promising results in the field of nondestructive testing of various materials. For example, ferromagnetic impurities in stainless steel formed by aging processes in the material can be detected with high probability, and cracks in conducting materials, for example aircraft parts, can be located using eddy current methods. Especially for the case of thick, highly conductive, or ferromagnetic materials, as well as sintered materials, it can be shown that a SQUID-based NDE system exhibits a much higher sensitivity compared to conventional eddy current NDE and ultrasonic testing.

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“…The advantage of the scanning SQUID microscope is its very high sensitivity. A comparison of relative sensitivity and resolution for the different techniques appears in [8]. Roughly speaking, the scanning SQUID microscope is orders of mapitude more sensitive to mapetic fields than the other techniques.…”

Section: Introductionmentioning

confidence: 98%

Design and applications of a scanning SQUID microscope

et al. 1995

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The scanning SQUID (Superconducting Quantum interference Device) microscope is an extremeiy sensitive instrument for imaging iocai magnetic fields. We describe one such instrument which combines a novel pivoting lever mechanism for coarse-scale imaging with a piezoelectric tube scanner for fine-scale scans. The magnetic field sensor is an integrated miniature SQUID magnetometer. This instrument has a demonstrated magnetic field sensitivity of <10 gauss/VHzat a spatial resolution of -10 fim. The design and operation of this scanning SQUID microscope are described, and several illustrations of the capabilities of this technique are presented. The absolute calibration of this instrument with an ideal point source, a single vortex trapped in a superconducting film, is shown. The use of this instrument for the first observation of half-integer flux quanta, in tricrystal thin-film rings of YBa2Cu30^_g, is described. The half-integer flux quantum effect is a general test of the symmetry of the superconducting order parameter. One such test rules out symmetry-independent mechanisms for the half-integer flux quantum effect, and proves that the order parameter in YBa^CUgO^.^ has lobes and nodes consistent with d-wave symmetry.

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Design and implementation of a scanning SQUID microscope

Cited by 69 publications

References 7 publications

Antiferromagnetic ordering in arrays of superconductingπ-rings

Antiferromagnetic ordering in arrays of superconductingπ-rings

SQUIDs: microscopes and nondestructive evaluation

Design and applications of a scanning SQUID microscope

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