摘要:

Using a high‐temperature superconducting YBa2Cu3O7−&dgr;Josephson‐junction harmonic mixer operated at 77 K and an analog phase‐locking loop, we have locked a 3 mm waveband Gunn oscillator to a synthesizer for harmonic numbers ranging from 10 to 52. The spectrum of the phase‐locked intermediate frequency reveals good phase‐locked quality even for the 48th harmonic mixing between the signal at 104.3 GHz and the local oscillator at about 2 GHz. Our experimental results show that a highTcsuperconducting harmonic mixer can work efficiently with high harmonic number for phase locking in the millimeter waveband. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.114216

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have fabricated YBa2Cu3O7−x–SrTiO3–YBa2Cu3O7−x(YBCO–STO–YBCO) trilayers, in which each layer is patterned photolithographically, capping the first YBCO film with aninsituSTO film. Atomic force microscopy demonstrates that the capping process dramatically improves the quality of the surface of the second layer, allowing the growth of an upper YBCO film with a substantially reduced level of low‐frequency flux noise. A magnetometer with a multiturn flux transformer coupled to a dc superconducting quantum interference device achieved a magnetic field noise of 74 fT Hz−1/2at 1 Hz, improving to 31 fT Hz−1/2at 1 kHz. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114217

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We describe the fabrication and characterization of super Schottky diodes which are used in the cryogenic part of a 3 GHz radio frequency superconducting quantum interference device (rf SQUID) readout electronics. The diodes were prepared on silicon wafers with ann‐doping level of 5×1024m−3. They exhibited sensitivities of 1500 V−1at 4.2 K, and a noise equivalent power of 2×10−15W/&sqrt;Hz was measured at 2.1 GHz. Using planar niobium 3 GHz rf SQUIDs and a cooled rf amplifier, experiments have been performed to investigate the feasibility of these super Schottky diodes for demodulation of the SQUID rf signal voltage. A simple cryogenic rf SQUID readout, employing two transistors and one super Schottky diode is described and investigated. Flux noise measurements in an open loop have been performed using this readout. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114218

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Demagnetization of porous green compacts consisting of iron‐alloy powder was observed under shock compression in the range of 4.0–13.5 GPa and 660–2040 K. The total reduction of the initial magnetization occurs under shock conditions with pressures exceeding 9 GPa and a temperature of 1300 K, and the possible mechanism for the observed demagnetization is consistent with the whole and/or partial &agr;‐ to &ggr;‐phase transition in the powder, depending on the localization of heat at the particle surfaces. The mechanism is also consistent with the anomalous low value of residual magnetic flux density of the recovered material which was overcompacted under undesirable conditions. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114219

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A large magnetoresistance ratio in excess of 10 000% (at 140 K,H=6 T) has been obtained in a sintered perovskitelike material with a composition of La0.60Y0.07Ca0.33MnOx. The doping of La–Ca–Mn–O with Y resulted in a decrease in the lattice parameter by ∼0.2%, and improved the magnetoresistance by an order of magnitude. The fact that such a large magnetoresistance can be obtained in a polycrystalline material implies that an epitaxial film growth may not be necessary for device applications, with fewer restrictions in substrate selection and processing parameters. Low field measurements at 77 K gave a magnetoresistance ratio of ∼6.5% atH=500 Oe in the La–Y–Ca–Mn–O sample. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114220

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Experiments to generate a thin composite Fe‐Ag film employing a sputter‐gas‐aggregation process are described. The magnetic properties are studied at low temperatures. In addition, the morphology is determined by high‐resolution transmission electron microscopy and the structure by using x‐ray diffraction and XAFS. Small clusters of about 11 A˚ in diameter are highly dispersed in an Ag matrix. They show the characteristics of interacting superparamagnets. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.114221

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In the present study magnetic and magnetostrictive properties of Tb(Fe1−xTx)2(T=Mn, Ga) compounds were examined by magnetic measurement, Mo¨ssbauer, and x‐ray study. Mo¨ssbauer study shows that the easy magnetization direction of the compounds may deviate slightly from the major axis of symmetry and the average isomer shift of the compounds decreases with increasing thexvalue, which was attributed to the charge transfer from 3delectrons of Mn atoms or 4pelectrons of Ga atoms into the 3dband of Fe. It was also found from x‐ray measurement that the spontaneous magnetostriction &lgr;111decreased due to Mn or Ga substitution, which can be understood on the basis of the single‐ion model. The increase of the polycrystal magnetostriction &lgr;sdue to Mn substitution was also found and can be ascribed to the increase of &lgr;100, which may be caused by the filling ofdbands due to substitution. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.114197

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A series of detailed calculations have been carried out using a stagnation flow model to examine the dependence of diamond growth rate on hydrocarbon injector location in dc arcjet reactors. It is predicted that, for methane feed, growth rate can be increased by as much as 75% by relocating the injector from a position near the plasma torch exit to one near the diamond surface, but outside the boundary layer. As the injector is moved towards the surface from the plasma torch, the concentrations of C and CH3present at the surface increase. When the injector is located within the boundary layer, the lower atomic hydrogen concentration and short residence time leave most of the injected CH4unreacted, causing growth rates to drop. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114198

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0003-6951    

DOI:10.1063/1.114199

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0003-6951    

DOI:10.1063/1.114200

出版商:AIP    

年代:1995

数据来源: AIP