摘要:

Variable‐thickness bridges (VTB’s) using Nb3Ge film have been investigated. In order to form a very short length bridge in the direction of the current flow and cause little damage to the superconducting properties, slant evaporation and anodization technique was used. The current–voltage characteristics, temperature dependence of critical current response to microwave irradiation were measured. One of the VTB’s whose length is estimated to be less than 100 nm showed microwave induced steps over a wide temperature range, from 6 to 18.3 K. The resistively shunted Josephson junction model is found to explain the behavior of the device well.

ISSN:0021-8979    

DOI:10.1063/1.332441

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A novel method of fabrication, as described in the following, was developed that ensures a good reproducibility of the junction. Namely, poly‐Si was deposited over a Si substrate whose surface had been previously thermally oxidized. The poly‐Si overlaid surface was then thermally oxidized. The bridge configuration of the junction was microprocessed by means of electron beam lithography. The fabricated configuration served as a mask in depositing the Nb layer on the substrate by means of rf sputtering to conclude the fabrication of a microbridge Josephson junction. The final process of the formation of the variable thickness microbridge configuration was readily carried out by placing another properly shaped mask over the masking bridge or by forming an SiO2layer over the poly‐Si layer. The SiO2layer was processed by selective plasma etching so that it would act as a mask over the bridge portion. The stabilization of the characteristics of the junction has been achieved due to the passivation which takes place during the heat treatment in atmosphere by forced oxidation of the Nb film surface and to the annealing of the film itself.

ISSN:0021-8979    

DOI:10.1063/1.332442

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An oscillator which utilizes the effect of the vortex motion in long Josephson tunnel junctions, i.e., flux flow, has been presented in millimeter and submillimeter wave region. An electromagnetic wave generated by the oscillator is detected with a small tunnel junction as a detector with a refined coupling configuration. Quantitative evaluation of the detected power showed that the detected power attained the value of 10−6W in the frequency range between 100 and 400 GHz, which is far superior to previous results. Frequency and magnetic field dependences of the present system were also measured, which showed that the output power was able to be controlled by the dc magnetic field. The present oscillator will be promising as the local oscillator in the integrated Josephson receiver systems.

ISSN:0021-8979    

DOI:10.1063/1.332443

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Transient flux flow voltage are observed when constant current is switched on in a type II superconductor at low magnetic fields. The nature of the transients is related to the method of formation of the flux line lattice. The transients are attributed to changes which occur in the flux line lattice as inhomogeneities created at the time of formation of the lattice move out of the sample as a result of flux flow. A model is developed to describe this process which includes the requirement that when dissimilar regions of flux move across the sample, the rate of flow must be the same for these regions, so that an equipotential exists across the sample width. For currents below the equilibrium critical current, excellent fits to this model are obtained for our data.

ISSN:0021-8979    

DOI:10.1063/1.332444

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Cu‐Nb3Sn microcomposite wires with additions of In, Ga, and Ge to the bronze and of Ta to the niobium have been produced by the hot‐powder‐metallurgical preparation method. The characteristic influences of the additives on the superconducting properties are discussed on the basis of measurements of critical current densities (up to fields of 19–22 T), critical temperatures as well as x‐ray microprobe analyses. Although all alloying additions are incorporated into the Nb3Sn filaments, significant enhancements of the upper critical field by 2 and 4 T, respectively, can only be achieved for Ta and Ga. With an appropriate choice of the preparation parameters the current‐carrying capability is considerably improved in the field range above 12 T. The optimized current densities reach values of 108and 2×107A/m2at 16 and 19 T, respectively.

ISSN:0021-8979    

DOI:10.1063/1.332445

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Detailed analyses of x‐ray rocking curves and ferromagnetic resonance spectra were used to characterize properties of ⟨111⟩‐oriented Gd, Tm, Ga:YIG films implanted with Ne+, He+, and H+2. For each implanted species the range of doses begins with easily analyzed effects and ends with paramagnetism or amorphousness. Ion energies were chosen to produce implanted layer thicknesses of 3000 to 6000 A˚. Profiles of normal strain, lateral strain, and damage were obtained. The normal strain increases with dose and near amorphousness is 2.5%, 3.4%, and 3.9% for Ne+, He+, and H+2, respectively. Lateral strain is 0 for all values of normal strain, implying absence of plastic flow. Comparison of these results with the reported decrease in lateral stress implies either a large reduction in Young’s modulus or a transition to rhombohedral equilibrium unit cell. Damage is modelled by a spherically‐symmetric Gaussian distribution of incoherent atomic displacements. Due to the use of (444), (888), and (880) reflections the sensitivity is greatest for thecsites occupied by Gd, Tm, and Y. The standard deviation of displacements increases linearly with strain with proportionality constant 0.25, 0.18, and 0.13 A˚/% for Ne+, He+, and H+2, respectively. For maximum strains up to 1.3% annealing in air reduces the strain without changing the shape of the profile. The behavior of the strain with annealing is nearly independent of implanted species or doses. After annealing at 600 °C the strain is 40% of the original value. Magnetic profiles obtained before and after annealing were compared with the strain profiles. The local change in anisotropy field &Dgr;Hkwith increasing strain shows an initially linear rise for both He+and Ne+. The slope is −4.1 kOe/%, in agreement with the magnetostriction effect estimated from the composition. For strain values between 1 and 1.5%, &Dgr;Hksaturates reaching peak values of −3.6 kOe for He+and −2.8 kOe for Ne+. At strain values near 2.3% for He+and 1.8% for Ne+, &Dgr;Hkdrops to nearly 0 and the material is paramagnetic. For peak strains greater than 1.3% for He+and 1.1% for Ne+the relation between uniaxial anisotropy and strain is not unique. The saturation magnetization 4&pgr;M, the ratio of exchange stiffness to magnetization (A/M) and the cubic anisotropy H1decrease with strain reaching 0 at 2.3% and 1.8% for He+and Ne+, respectively. At these strain values the damping coefficient &agr; is 50% and 80% greater than bulk value for He+and Ne+, respectively. For higher observed strains the material remains paramagnetic. Upon annealing of samples implanted with low doses of Ne+and He+the anisotropy field follows uniquely the behavior with strain for unannealed material. At 600 °C the magnetization returns to bulk value but the ratioA/Mremains 20% low. For H+2implantation the total &Dgr;Hkconsists of a magnetostrictive contribution due to strain and of a comparable excess contribution associated with the local concentration of hydrogen. The profile of excess &Dgr;Hkagrees with calculated LSS range. The presence of hydrogen results in a reduction of 4&pgr;M not attributable to strain or damage. For a peak strain of 0.60% and a peak total &Dgr;Hkof −4.5 kOe, the magnetization is only 40% of bulk value. After annealing up to 350 °C the excess &Dgr;Hkdiminishes and redistributes itself to the regions neighboring the peak damage. At 400 °C the excess is nearly 0. For higher annealing temperatures the only component of &Dgr;Hkis magnetostrictive. At 600 °C, the magnetization, the ratioA/M, and &agr; return to bulk values.

ISSN:0021-8979    

DOI:10.1063/1.332446

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

This article discusses the magnetic properties observed in porous glasses impregnated with metal carbonyls after exposure to light. In the photolyzed and consolidated glasses both superparamagnetic and single domain ferrimagnetic particles were found to be present, with the single domain particles having an exceedingly high coercive force. The concentration ratio between superparamagnetic and single domain particles depends strongly on temperature. An analysis of the observed phenomena is given.

ISSN:0021-8979    

DOI:10.1063/1.332447

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Three ferrofluids, consisting of suspensions of Fe3O4particles of &bartil;100–200 A˚ diameter in diester, hydrocarbon, and water have been investigated at temperatures 4.2–300 K by means of Mo¨ssbauer effect and magnetic measurements. The magnetic data displays almost all the features observed in the spin glasses. The Ne´el model is used to explain the behavior of the fluids. From the temperature variation of the initial susceptibility and the isothermal remanence, K=(3.5±0.7)×105erg/cc andD0=(80±5) A˚ are obtained for the anisotropy constant and the median diameter, respectively, of the diester based ferrofluid. The ac susceptibility gives K=3×105erg/cc andD0=92 A˚. For the water based ferrofluid measurements give K=1.5×105erg/cc. Values obtained from Mo¨ssbauer measurements forKandD0agree with those obtained from magnetization–susceptibility data.

ISSN:0021-8979    

DOI:10.1063/1.332448

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The magnetization distributions in the neighborhood of the corners of soft ferromagnetic geometries are both theoretically and experimentally investigated. We have previously introduced the wall cluster—a collection of domain walls having one intersection line, the so‐called cluster knot, in common—as a novel concept to get a better grip on the complex process of domain‐structure conversions. These wall clusters can be classified according to the positions of the cluster knots into the free, the edge, and the corner clusters. The edge and free clusters, whose cluster knots coincide with one single edge and with no any edge of the geometry, respectively, have been discussed elsewhere. Here the micromagnetic characteristics of a corner cluster in thin layers are discussed, while the systems approach to corner clusters, in which the cluster is treated as a system of walls, is left to Part II. Bear in mind that the torque equilibrium is dominated by the total Maxwell field, composed of the external and demagnetizing field near the domain walls and the edges of the geometry. From this starting point, it is shown that no domain wall is present in a region in which the total field is not zero. Similarly, it is demonstrated that no line space‐charge‐density singularities can appear at a cluster knot. As a consequence, the magnetization in the domains can be divided into so‐called rotation segments and uniform sectors, in which the magnetization rotates circularly around the cluster knot or is quasiuniform, respectively. Space‐charge‐density singularities occur at the bounding surfaces of the geometry. This surface‐charge density generates a singularity in the total field in case this density does not reduce to zero in the corner. No domain wall can be present in the corner in these circumstances, so that the cluster knot is either shoved along one of the bounding edges of the corner or it disengages itself from the edges and the corner cluster is tranformed into a free cluster. It is experimentally demonstrated that these singularities in the field often, but not always, occur in the corner when an external field is applied. These and other above‐mentioned statements are also supported by experimental evidence.

ISSN:0021-8979    

DOI:10.1063/1.332449

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

This report describes a recently developed domain‐wall‐oscillation spectrum analyzer and the results of some sensitive quantitative measurements of domain wall motion response in underdamped garnet films. Objects of study include periodic bubble domain lattices and periodic stripe patterns. Wall displacements as small as 5 A˚ (only a few percent of the wall width) are detectable, thus allowing observation of resonance multiplets due to wall flexure not seen by other techniques. The data presented here are taken in the linear region at low drive (well below onset of velocity saturation) in thin film samples of Gd, Ga:YIG grown epitaxially on Gd3Ga5O12. The domain wall resonance linewidth determination of the Gilbert damping parameter agrees with monodomain ferromagnetic resonance, resolving previous discrepancies with respect to effective mass and damping coefficient found in free oscillations following pulsed excitations in thin films and in complex susceptibility spectra in thick single crystal plates. Losses and nonlinearities due to coercivity appear suppressed in dense domain configurations by the presence of strong restoring forces. Comparison of our theory and experiments show that the rigid‐wall model accounts well for the first resonance, including its dependence on lattice period and external field applied normal to the film. The Do¨ring mass, however, needs correction by numerical calculations for effects of stray fields. Empirical andapriorirestoring‐force coefficients agree very well with our observed resonance frequencies.

ISSN:0021-8979    

DOI:10.1063/1.332450

出版商:AIP    

年代:1983

数据来源: AIP