摘要:

We have designed and fabricated a low‐noise dc superconducting quantum interference device (SQUID) magnetometer that is integrated on a 4×4 mm2chip. The white flux noise of the magnetometer measured in a flux‐locked‐loop mode using simple, direct‐coupled electronics with additional positive feedback (APF) is 6.4×10−7&Fgr;0/&sqrt;Hz. The corresponding white flux density noise is 3.9 fT/&sqrt;Hz. The SQUID flux‐to‐voltage transfer function with APF is enhanced to 4.7 mV/&Fgr;0at the optimal working point, thereby significantly reducing the preamplifier contribution to the total noise. A maximum feedback field of 65 nT for frequencies up to 300 Hz and a maximum slew rate of 120 &mgr;T/s at 300 Hz have been attained using a two‐pole integrator.

ISSN:0003-6951    

DOI:10.1063/1.105974

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The evolution of YBCO film growth with thickness at various oxygen pressures was observed byinsitusynchrotron x‐ray diffraction in real time. When the films were deposited at 2 A˚/s and 730 °C under higher oxygen partial pressures (in an Ar/O2mixture of 90 mTorr), the nucleation was observed to havec‐axis orientation. After the films reached a critical thickness, the growth of the YBCO film changed fromcaxis toaaxis and then propagated epitaxially. This provides evidence thata‐axis epitaxial growth nucleates on ac‐axis base. The critical thickness reflects the competition between the growth of thecandaaxes, which is determined by the oxygen partial pressure in the process of thin‐film formation. Thea‐axis oriented films showed a very sharp rocking curve (less than 0.1°) which indicates a very high structural quality. For very low oxygen partial pressures, theinsitugrowth process was very similar, but the initial nuclei involve a second phase mixed with a small amount ofc‐axis ‘‘123’’ phase. The nucleation and growth mechanisms ofinsituYBCO films are discussed.

ISSN:0003-6951    

DOI:10.1063/1.105975

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Light‐ion irradiation can controllably reduce the critical current density of high‐temperature superconductor thin films. Reported here is the behavior of ErBa2Cu3O7films patterned into microbridge dc superconducting quantum interference device (SQUID) structures and irradiated with a rastered high‐energy focused ion beam of 70 nm diameter. The resultant SQUIDs have demonstrated up to 51% critical current modulation at 46 K. Microbridges with appropriate critical currents manifest Josephson‐like behavior in the form of well‐defined Shapiro steps appearing with microwave radiation. TheIcRnproducts of these microbridges are typically a few millivolts and the temperature dependence of their normal‐state resistance is consistent with conduction through metallic filaments.

ISSN:0003-6951    

DOI:10.1063/1.105976

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Bismuth‐substituted yttrium iron garnet (Bi:YIG) films were deposited on gadolinium gallium garnet substrate by laser ablation using the ArF excimer laser. This is the first report on the preparation of Bi‐substituted YIG films by laser ablation. Films have a garnet single phase above the substrate temperature of 490 °C, and the film composition does not deviate largely from the target composition and it is almost constant in the temperature range between 490 and 580 °C. The saturation magnetization of the film is 1500 G at room temperature. Faraday rotation angle &thgr;Fat a wavelength of 830 nm at room temperature is −0.3×104°/cm.

ISSN:0003-6951    

DOI:10.1063/1.105977

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Fe‐Cu‐Co sandwiches have been grown on glass and silicon substrates using electron beam evaporation. Because the typical coercive field of a thin Co film is higher than that of a typical Fe film, the magnetization curves of these sandwiches show clearly the separate, sequential reversal of the Fe and Co moments as a function of applied field. In the applied field region where the moments of the two magnetic layers are antialigned, the spin‐valve magnetoresistance shows a peak of over 3% in amplitude at room temperature.

ISSN:0003-6951    

DOI:10.1063/1.105978

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

By applying voltage pulses of about −5 V at the tip of a scanning tunneling microscope triangular structures have been created on the atomically flat WSe2surface. The evolution from a cluster‐like structure directly after the pulse to an equilateral triangle occurs within minutes. The growth of the triangles has been investigated for times up to 1 h. For a given orientation of the substrate all the triangles have the same orientation thereby reducing the sixfold symmetry at the atomic Se surface to the threefold symmetry of a full molecular WSe2layer.

ISSN:0003-6951    

DOI:10.1063/1.105979

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We observe, for the first time in a laboratory, the formation of decursors at intersections of planar surfaces with powerful blast waves. The blast waves, which have hundreds‐kilobar overpressures, are created by rapid ablation of material heated with an intense laser beam.

ISSN:0003-6951    

DOI:10.1063/1.105980

出版商:AIP    

年代:1991

数据来源: AIP