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The magnetic properties of Au/Ni/Si(100) films with Ni thicknesses of 8–200 A are studied at T=77 K using a scanning magnetic microscope with a thin-film high-temperature dc SQUID. It is found that the Ni films, with an area of 0.6×0.6 mm, which are thicker than 26 A have a single-domain structure with the magnetic moment oriented in the plane of the film and a saturation magnetization close to 0.17 MA/m. For films less than 26 A thick, the magnetization of the film is found to drop sharply.

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.

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.

We have developed two versions of magnetic flux microscope which use an YBCO thin film bicrystal do SQUID to image the two-dimensional distribution of magnetic field. With the size of the inner hole of the SQUID close to 30 μm a spatial resolution of about 200 μm and a field of view 3×4 mm 2 have been obtained. The equivalent magnetic field noise in the SQUID ranges from 100 pT/Hz −1/2 at 1 Hz to 10 pT/ Hz −1/2 at 100 Hz. We have employed the microscope to image 50 μA 110 Hz ac currents flowing in the thin parallel wires.

We have applied a developed HTS dc SQUID based magnetic microscope for study of the magnetic properties of ultrathin Ni films. A magnetic moment sensitivity close to 10/sup -15/ A.m/sup 2//Hz/sup 1/2/ has been obtained at 77 K. The space resolution was determined at level of 100 /spl mu/m by the separation between the SQUID and the studied film surface. One-domain structure, in-plane orientation of magnetic moment and ferromagnetic-like ordering in 26 /spl Aring/ thick film were found. An absolute value of the film magnetic moment has been estimated.

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.

We have applied a scanning HTS (high-temperature superconductor) de SQUID (superconducting quantum interference device) -based magnetic microscope to study the magnetic properties of Au/Ni/Si(100) films in the thickness range from 8 to 200 Angstrom at T = 77 K. A one-domain structure with in-plane orientation of the magnetic moment was found for film thicknesses exceeding 26 Angstrom. A drastic decrease of the magnetization of the film was detected when the thickness is less than 26 Angstrom.