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26 Dec 1994

Volume 65, Issue 26, pp. 3305-3416

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Single layer YBa2Cu3O7 radio frequency SQUID magnetometers with direct‐coupled pickup coils and flip‐chip flux transformers

Y. Zhang, U. Krüger, R. Kutzner, R. Wördenweber, J. Schubert, W. Zander, E. Sodtke, A. I. Braginski, and M. Strupp

Appl. Phys. Lett. 65, 3380 (1994); http://dx.doi.org/10.1063/1.112398 (3 pages) | Cited 10 times

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Our aim has been to further improve the magnetic field resolution, BN, of single‐layer rf SQUID magnetometers operating in liquid nitrogen. Following the approaches recently introduced in dc SQUIDs, we tested designs with direct‐coupled pickup coils having an area Ap=0.6 to 0.8 cm2, and a single‐layer thin‐film flip‐chip flux transformer with Ap=16 cm2. In conditions of still suboptimal coupling between SQUID and the 150 MHz tank circuit, we attained BN≂90 fT/Hz1/2 above 3–4 Hz at Ap=0.8 cm2, and BN≂24 fT/Hz1/2 above 0.5 Hz when Ap=16 cm2. For rf SQUID with lumped‐element tank circuit, we project the lower BN limit to be ≤50 fT/Hz1/2 at Ap≤1 cm2. This might be attainable through further coupling optimization, and increase of tank frequency to the highest possible value of ≥500 MHz. © 1994 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)

Thickness dependence of La2−xSrxCuO4 films

Marta Z. Cieplak, M. Berkowski, S. Guha, E. Cheng, A. S. Vagelos, D. J. Rabinowitz, B. Wu, I. E. Trofimov, and P. Lindenfeld

Appl. Phys. Lett. 65, 3383 (1994); http://dx.doi.org/10.1063/1.112399 (3 pages) | Cited 32 times

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Pulsed laser deposition was used to grow c‐axis aligned films of La2−xSrxCuO4−δ, with Sr content, x, in the range of 0.03 to 0.2, on substrates prepared from single‐crystalline SrLaAlO4, with a lattice mismatch of 0.5%. The thickness dependence of Tc0, the temperature at which the resistance falls to zero, is much reduced compared to that of films deposited on SrTiO3, where the lattice mismatch is 3.4%. The maximum Tc0 is achieved at x=0.15 for both types of substrates. While the thickness dependence is related to the strain resulting from the lattice mismatch, the value of the maximum Tc0 is determined by the oxygen concentration. © 1994 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Fg Pulsed laser ablation deposition
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.72.-h Cuprate superconductors

Crystal morphology and three‐dimensional‐like growth model of DyBa2Cu3O7−d superconducting materials synthesized in situ in 0.6 T

R. Cloots, N. Vandewalle, and M. Ausloos

Appl. Phys. Lett. 65, 3386 (1994); http://dx.doi.org/10.1063/1.113025 (3 pages) | Cited 6 times

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This report discusses the crystal growth mechanism of 123 superconducting ceramics from scanning electron micrographs made on DyBa2Cu3O7−d superconducting materials synthesized by peritectic recombination under a magnetic field. Such a synthesis procedure is used only here in order to enhance the growth features of textured materials. The micrographs reveal that the crystal growth model must be strictly tridimensional. The proposed model, followed by computer simulations, can then explain all the microstructure data reported for such textured materials. The preferred growth direction in the a–b planes could also be expected to be the 〈100〉 direction. © 1994 American Institute of Physics.
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81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
81.10.Fq Growth from melts; zone melting and refining
74.72.-h Cuprate superconductors
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors

Electrical tuning of the kinetic inductance of high temperature superconductors

S. Cho, H. Erlig, A. Z. Kain, H. R. Fetterman, G.‐C. Liang, M. E. Johansson, B. F. Cole, and R. S. Withers

Appl. Phys. Lett. 65, 3389 (1994); http://dx.doi.org/10.1063/1.112400 (3 pages) | Cited 10 times

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A current controlled delay in the time of flight of electrical picosecond pulses in a YBa2Cu3O7 spiral delay line has been investigated using optoelectronic sampling techniques. The transmission line is a microwave stripline on the LaAlO3 substrate and is passivated with the contact pads open. The measured delay time clearly shows a squared dependence on the applied current, in good agreement with Ginzburg–Landau theory for the case of a uniform current density through a thin film. © 1994 American Institute of Physics.
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85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
84.40.Az Waveguides, transmission lines, striplines
74.78.-w Superconducting films and low-dimensional structures

Effect of Ag2O addition in Y0.9Ca0.1Ba2Cu4O8 on the contact characteristics of Y0.9Ca0.1Ba2Cu4O8/Ag interface

Y. C. Chen, C. K. Yang, T. H. Meen, and H. D. Yang

Appl. Phys. Lett. 65, 3392 (1994); http://dx.doi.org/10.1063/1.112401 (3 pages) | Cited 1 time

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Effects of an Ag2O addition in Y0.9Ca0.1Ba2Cu4O8 on the contact characteristics of Y0.9Ca0.1Ba2Cu4O8/Ag interfaces have been investigated by the measurement of contact resistivity. The lowest ohmic‐contact resistivity about 4.55×10−5 Ω cm2 at 300 K and less than 10−8 Ω cm2 below Tc for Ag2O‐free system are observed by annealing at 600 °C for 1 h under one oxygen atmosphere. With addition of 25 wt % Ag2O in Y0.9Ca0.1Ba2Cu4O8, the optimal annealing condition for the lowest ohmic‐contact for Y0.9Ca0.1Ba2Cu4O8/Ag interface can be achieved without any thermal annealing just by the addition of 25 wt % Ag2O in Y0.9Ca0.1Ba2Cu4O8. These results indicate that the addition of Ag2O can upgrade effectively the characteristics of Y0.9Ca0.1Ba2Cu4O8/Ag interfaces to get the better ohmic contact even without annealing, resulting in a lower annealing temperature and contact resistivity. © 1994 American Institute of Physics.  
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
73.40.Cg Contact resistance, contact potential
74.72.-h Cuprate superconductors

Coexistence of grains with differing orthorhombicity in high quality YBa2Cu3O7−δ thin films

E. I. de Obaldia, K. F. Ludwig, S. J. Berkowitz, A. M. Clark, W. J. Skocpol, P. M. Mankiewich, D. A. Rudman, A. Roshko, R. Moerman, L. Vale, and R. H. Ono

Appl. Phys. Lett. 65, 3395 (1994); http://dx.doi.org/10.1063/1.112402 (3 pages) | Cited 2 times

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High quality films of YBa2Cu3O7−δ on LaAlO3 have been grown by pulsed‐laser deposition at oxygen pressures of 3.4–54 Pa (25–400 mTorr). X‐ray diffraction reveals the coexistence of grains that align with the substrate axes (axial grains) and grains that are rotated by 0.4° from the substrate axes (diagonal grains). The axial grains are tetragonal while the diagonal grains achieve lattice parameters close to bulk YBa2Cu3O7. The relative proportion of axial grains accounts for the measured variations of normal‐state conductance and superconducting critical current density from film to film, based on a simple two‐dimensional model of randomly positioned, insulating axial grains. © 1994 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Fg Pulsed laser ablation deposition
74.25.Sv Critical currents
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors

Optical mixing in a patterned YBa2Cu3O7−δ thin film

M. Lindgren, M. A. Zorin, V. Trifonov, M. Danerud, D. Winkler, B. S. Karasik, G. N. Gol’tsman, and E. M. Gershenzon

Appl. Phys. Lett. 65, 3398 (1994); http://dx.doi.org/10.1063/1.112405 (3 pages) | Cited 17 times

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Mixing of 1.56 μm infrared radiation from two lasers in a high quality YBa2Cu3O7−δ thin film, patterned to parallel strips, was demonstrated. A mixer bandwidth of 18 GHz, limited by the measurement system, was obtained. A model based on nonequilibrium electron heating gives a good fit to the data and predicts an intrinsic mixer bandwidth in excess of 100 GHz, operating in the whole infrared spectrum. Reduction of bolometric effects and ways to decrease the conversion loss of the mixer is discussed. The minimum conversion loss is expected to be ∼10 dB. © 1994 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
85.60.Gz Photodetectors (including infrared and CCD detectors)

Superconducting quantum interference device magnetometry during ultrahigh vacuum growth

D. P. Pappas, G. A. Prinz, and M. B. Ketchen

Appl. Phys. Lett. 65, 3401 (1994); http://dx.doi.org/10.1063/1.112406 (3 pages) | Cited 8 times

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An in situ study of the absolute magnetic moment of thin ferromagnetic films grown in ultrahigh vacuum (UHV) is described. The moments are measured using a newly innovated technique, rotating sample superconducting quantum interference device (SQUID) magnetometry (RSSM), in which the sample is spun at low frequency close to an ex situ second derivative superconducting pickup loop structure coupled to a rf SQUID. The sensitivity of the measurements is ≊10−6 emu, which corresponds to 1/10 of an atomic layer of Fe over a 0.5 cm2 area, and the geometry of the pickup loops makes the magnetometer very insensitive to background laboratory noise. The moment of Cr grown on Fe was measured. It was determined that the first two layers of Cr have an average moment of 0.75 μB per atom, and are antiferromagnetically aligned to the Fe film moment. The simplicity of RSSM and the fact that the absolute moment is measured makes this a powerful new approach for characterization of magnetic samples in UHV. © 1994 American Institute of Physics.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.70.Rf Surface magnetism
07.55.-w Magnetic instruments and components
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Influence of heat treatment on the structure and magnetic properties of sputtered BaCoTiFe10O19 films

B. X. Gu, H. Y. Zhang, H. R. Zhai, M. Lu, S. Y. Zhang, and Y. Z. Maio

Appl. Phys. Lett. 65, 3404 (1994); http://dx.doi.org/10.1063/1.112407 (3 pages) | Cited 1 time

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BaCoTiFe10O19 films were prepared by sputtering. The as‐sputtered films are amorphus and have a magnetization of 5 emu/cm3 and a coercivity of 700 Oe at room temperature. Compared with bulk BaCoTiFe10O19 hexaferrites, the magnetization is much smaller, but the coercivity is higher. After annealing at about 750 °C in an oxygen atmosphere, the films crystallize into an M‐type hexagonal ferrite with a preferred orientation of the (110) plane being parallel to the film surface. The magnetization increases rapidly to 320 emu/cm3, but the coercivity decreases to 100 Oe. The amorphous samples with a large amount of Fe3+ ions show no ferromagnetic magnetic resonance spectra. After crystallization a well‐defined ferromagnetic resonance spectrum occurs. © 1994 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
81.15.Cd Deposition by sputtering
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
81.40.Rs Electrical and magnetic properties related to treatment conditions

Just‐on‐surface magnetic force microscopy

Sumio Hosaka, Atsushi Kikukawa, Yukio Honda, and Tsuyoshi Hasegawa

Appl. Phys. Lett. 65, 3407 (1994); http://dx.doi.org/10.1063/1.112987 (3 pages) | Cited 6 times

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We propose a just‐on‐surface magnetic force microscope (JS‐MFM) for advanced spatial resolution of magnetic stray field image. In this letter, we describe that the JS‐MFM provides better resolution of the stray field image than that in conventional magnetic force microscope, theoretically and experimentally. In the rough estimations, magnetic stray field image just on the surface provides higher resolution of less than 10 nm. In the experiments, initial results demonstrate that JS‐MFM can observe a localized surface magnetic stray field caused by small magnetizations in the perpendicularly recorded magnetic domains with a high resolution of around 10 nm. © 1994 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
75.70.Rf Surface magnetism

Shear stresses in magnetorheological fluids: Role of magnetic saturation

J. M. Ginder and L. C. Davis

Appl. Phys. Lett. 65, 3410 (1994); http://dx.doi.org/10.1063/1.112408 (3 pages) | Cited 80 times

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The interparticle forces and resulting shear stresses in a magnetorheological fluid are calculated. The field due to a linear chain of particles in a fixed average magnetic induction Bave is determined from a finite element analysis in which the nonlinearity and saturation of the particle magnetization are incorporated. The shear stresses are then computed from the field using Maxwell’s stress tensor. The stresses obtained for all but the lowest magnetic inductions are controlled by the saturation of the magnetization in the contact regions of each particle. Identifying the maximum shear stress as a function of shear strain with the yield stress gives values in agreement with results reported for typical fluids. For high magnetic inductions the yield stress plateaus due to the complete saturation of the particle magnetization; the stress scales as the square of the saturation magnetization in this regime. © 1994 American Institute of Physics.
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83.80.Gv Electro- and magnetorheological fluids
83.60.Np Effects of electric and magnetic fields
75.50.Mm Magnetic liquids
75.50.Tt Fine-particle systems; nanocrystalline materials

Nanosecond time‐resolved interferometric study on morphological dynamics of doped poly(methyl methacrylate) film upon laser ablation

Hiroshi Furutani, Hiroshi Fukumura, and Hiroshi Masuhara

Appl. Phys. Lett. 65, 3413 (1994); http://dx.doi.org/10.1063/1.112409 (3 pages) | Cited 15 times

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A highly sensitive nanosecond time‐resolved interferometry was developed and applied to study dynamics of morphological changes of a thin poly(methyl methacrylate) film doped with biphenyl upon laser ablation. It was confirmed that morphological changes started during a nanosecond excitation laser pulse and then followed by an ejection of ablated polymer fragments. Even below the ablation threshold, a transient expansion of the polymer film, followed by slow contraction, was observed. New features of laser ablation dynamics were clarified. © 1994 American Institute of Physics.  
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79.20.Ds Laser-beam impact phenomena
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
FREE

Erratum: ‘‘Charge sensitivity of a single electron transistor’’ [Appl. Phys. Lett. 65, 1847 (1994)]

Ulrik Hanke, Yu. M. Galperin, and K. A. Chao

Appl. Phys. Lett. 65, 3416 (1994); http://dx.doi.org/10.1063/1.113094 (1 page)

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Abstract Unavailable
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
72.70.+m Noise processes and phenomena
73.40.Gk Tunneling
99.10.Cd Errata
FREE

Erratum: ‘‘Electron and hole mobilities in lightly doped silicon’’ [Appl. Phys. Lett. 64, 2007 (1994)]

Konstantinos Misiakos and Dimitris Tsamakis

Appl. Phys. Lett. 65, 3416 (1994); http://dx.doi.org/10.1063/1.113095 (1 page)

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Abstract Unavailable
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68.35.Fx Diffusion; interface formation
68.55.Nq Composition and phase identification
79.70.+q Field emission, ionization, evaporation, and desorption
68.37.Vj Field emission and field-ion microscopy
99.10.Cd Errata
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