L.V. Matveets

Magnetic field maps of YBCO thin films obtained by scanning SQUID microscopy for HTSC microelectronics

Scanning SQUID microscopy has been extended to record current-induced magnetic field maps of superconductor topologies based on YBCO film structures. The technique described can be used as a powerful tool for the diagnostics of superconductor integrated circuits and highly sensitive bolometers. This kind of diagnostics predicts the degree of integration which can be achieved at the modern level of HTSC microelectronics technology. One would expect an overall yield of 100-element chips at a level of in the production of superconducting YBCO/MgO bolometers.

Flux guide for high-Tc SQUID microscope with high spatial resolution

Abstract Magnetic properties of amorphous ferromagnetic wires serving as a magnetic flux guide for the high- T c SQUID microscope are investigated. A mathematical model of a flux guide operation was developed on the base of integral equation methods. It is shown that when the flux guide is used in combination with the SQUID the integral of magnetic potential along the flux guide is the main measured value. Experimental results received with the use of the scanning high- T c SQUID microscope for liquid-nitrogen cooled samples are in good agreement with the proposed model.

HTS scanning SQUID microscope with high spatial resolution for room temperature samples

A scanning HTS SQUID microscope for magnetic imaging samples at room temperature and atmospheric pressure has been developed. A sensor for the microscope was completed by a bicrystal dc SQUID and a needle made of soft magnetic material, which serves as a magnetic flux guide (MFG). This sensor has allowed magnetic imaging of the warm samples with spatial resolution of the order of 100 μm. Line scans of magnetic field produced by the current-carrying wires are measured and compared with results of a numerical modeling. The influence of the MFG on the image details has been studied.

SQUID microscope for magnetic structure visualization in magnetoimpedance elements

An attempt to apply a SQUID microscope for visualization of magnetic structure in giant magnetic impedance (GMI) elements was undertaken. The measurements were carried out on the 1/spl times/10/sup -3/ mm thick permalloy strip with the in-plane sizes 6 mm/spl times/0.3 mm. The topography of the vertical component of magnetic field was imaged with a high spatial resolution close to 30/spl times/10/sup -3/ mm over the central part of a sample. The images taken in the applied magnetic field varied over the range /spl plusmn/4 kA/m reveal the domain structure with anisotropy perpendicular to longitudinal sample axis.

Direct-coupled electronics for high-temperature superconductor DC SQUID-based magnetometer

A low-volume, high-performance, direct-coupled electronic system for high-T/sub c/ dc SQUID magnetometers has been developed and tested. This system is based on a liquid nitrogen-cooled amplifier and a modified integrator. The amplifier has a white noise voltage level close to 0.25 nVHz/sup - 1/2 /, a current noise of the order of 3 pAHz/sup - 1/2 /, a gain equal to 3000, a 3 dB bandwidth of about 370 kHz, and a package volume less than 3 cm/sup 3/. The modified integrator has an input resistance of the order to 10 k/spl Omega/ and a considerably high output drive current of about 30 mA. This unique combination results in the typical electronic 3 dB bandwidth of about 1 MHz, a dynamic range of /spl plusmn/5/spl times/10/sup 6/ Hz/sup - 1/2 / for frequencies up to 1.6 kHz, and a slew rate of 1/spl times/10/sub 6/ flux quanta/s in a wide signal frequency range for a middle-quality high-T/sub c/ dc SQUID sensor.

Study of amorphous ferromagnetic microwires using a scanning SQUID microscope

Abstract The magnetic properties of amorphous ferromagnetic 30–50-μm diameter microwires produced by means of spinning process are studied both experimentally and theoretically. The magnetic images of the microwire are measured at 77 K with the high-spatial resolution scanning SQUID microscope in an axial magnetic field up to 103 A/m. The values of the local magnetic fields produced by the microwire in remnant state are typically a few μT at a distance 50–100 μm far from the sample. It is shown that the wires domain structure calculated numerically is in a qualitative agreement with the magnetic images obtained experimentally.

A direct readout high-T/sub c/ dc SQUID electronics with ac bias and a liquid-nitrogen-cooled preamplifier

Direct readout dc SQUID electronics based on a liquid-nitrogen-cooled preamplifier and alternating current bias was developed. The preamplifier with an intrinsic voltage noise of 0.18 nV/Hz/sup 1/2/ was used as the first stage of this electronics. A mathematical description of the noise suppression by this electronics was done. Low-frequency noise was reduced by a factor of 6 at 1 Hz by this technique.

Directly coupled electronics for HTSC DC SQUID based magnetometer

A low-volume high-performance directly coupled electronics for the high-T/sub c/ DC SQUID magnetometers has been developed and tested. This electronics is based on a liquid nitrogen cooled preamplifier with the white noise level close to 0.25 nV/Hz/sup 1/2/, packed in the volume less than 3 cm/sup 3/ and results in a typical 3 dB bandwidth of about 1 MHz, maximum dynamic range 140 dB for frequencies up to 1 kHz and the maximum slew rate more than 10/sup 6/ flux quanta in second with a middle-quality DC SQUID sensor.

Detection properties of thin film high-Tc bridges on bicrystal substrate

Abstract We report on the detection properties of the Josephson grain-boundary junctions fabricated from an epitaxial YBa 2 Cu 3 O 7−x thin film on a bicrystal SrTiO 3 substrate at 37–70 GHz and 77 K.