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23 Dec 2002

Volume 81, Issue 26, pp. 4895-5074

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Superconducting single-electron transistor coupled to a locally tunable electromagnetic environment

W. Lu, A. J. Rimberg, and K. D. Maranowski

Appl. Phys. Lett. 81, 4976 (2002); http://dx.doi.org/10.1063/1.1530731 (3 pages) | Cited 5 times

Online Publication Date: 17 December 2002

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We have developed a system consisting of a superconducting single-electron transistor (S-SET) coupled to a two-dimensional electron gas (2DEG), for which the dissipation can be tuned in the immediate vicinity of the S-SET. Such tuning can be performed easily, and provides access to a significant range of environmental impedances. For temperatures above 100 mK, we find qualitative agreement between measured changes in the S-SET conductance versus dissipation and a model incorporating electromagnetic fluctuations in both the S-SET leads and the 2DEG. © 2002 American Institute of Physics.
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85.25.-j Superconducting devices
85.35.Gv Single electron devices
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.50.+r Tunneling phenomena; Josephson effects

Influence of LaAlO3 surface topography on rf current distribution in superconducting microwave devices

A. P. Zhuravel, A. V. Ustinov, K. S. Harshavardhan, and Steven M. Anlage

Appl. Phys. Lett. 81, 4979 (2002); http://dx.doi.org/10.1063/1.1530753 (3 pages) | Cited 15 times

Online Publication Date: 17 December 2002

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A laser scanning microscope with a thermal spot size of about 4 μm is used to measure a quantity proportional to the rf current density in an operating superconducting coplanar waveguide microwave resonator. The twinning of the LaAlO3 substrate produces a meandering of the current at the edges due to irregularities in the wet etching of the YBa2Cu3O7−δ film associated with substrate twin domain blocks, and an ( ∼ 20%) enhancement of the rf photoresponse at these locations. These irregularities are candidates for enhanced nonlinear response from the device. © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors
85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Mm Grain and twin boundaries

Highly crystallized as-grown smooth and superconducting MgB2 films by molecular-beam epitaxy

A. J. M. van Erven, T. H. Kim, M. Muenzenberg, and J. S. Moodera

Appl. Phys. Lett. 81, 4982 (2002); http://dx.doi.org/10.1063/1.1530732 (3 pages) | Cited 38 times

Online Publication Date: 17 December 2002

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We have investigated the growth of superconductive thin films of magnesium diboride (MgB2) by molecular-beam epitaxy. A Si(111) substrate with a seed layer of MgO was used for the growth of these films by varying parameters such as the growth temperature, Mg:B flux ratio and deposition rate as well as the background pressure. It was found that highly crystallized films could already form at 250 °C; however, only in a narrow window of growth parameters. The highest critical temperature of 35.2 K with a sharp transition (ΔTC of 0.5 K) was observed for films grown at 300 °C. Using a capping layer of MgO proved to be highly beneficial for the preservation and the smoothness of these films. Together with the fact that MgO proved to be a good seed layer for thin films of MgB2 makes it an ideal candidate for growing all epitaxial MgB2 Josephson junctions. © 2002 American Institute of Physics.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.10.+v Occurrence, potential candidates

Field-induced anisotropic nitrogen distribution as the source of uniaxial magnetic anisotropy in (Fe0.98Al0.02)1−δNδ films

Y-K. Liu, M. H. Kryder, and V. G. Harris

Appl. Phys. Lett. 81, 4985 (2002); http://dx.doi.org/10.1063/1.1531224 (3 pages) | Cited 1 time

Online Publication Date: 17 December 2002

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Extended x-ray absorption fine structure is employed to describe a physical fingerprint that distinguishes the easy and hard in-plane magnetic axes in (Fe0.98Al0.02)1−δNδ films. This fingerprint manifests as an anisotropic strain field about the Fe atom and is shown to scale with magnetic anisotropy energy as δ increases. We propose this effect is due to an anisotropic distribution of N atoms caused by the application of a magnetic field during growth. © 2002 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
78.70.Dm X-ray absorption spectra

Charge redistribution in YBa2Cu3O7−d probed by Raman spectroscopy: CuO2-plane phonon as a probe of carrier dynamics in the CuO2 plane

Minoru Osada, Masato Kakihana, Mikael Käll, and Lars Börjesson

Appl. Phys. Lett. 81, 4988 (2002); http://dx.doi.org/10.1063/1.1529082 (3 pages)

Online Publication Date: 17 December 2002

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Raman-scattering spectra were investigated for the Y1−xCaxBa2Cu3−yCoyO7−d system which undergoes a metal-to-insulator transition under variation of carrier concentration. As the system approaches the metal-to-insulator phase boundary, the intensity of CuO2-plane phonon modes decreases. We found that the intensity of the CuO2-plane mode scales with the inverse of the hole concentration within the CuO2 conducting planes. A remarkable correlation is found between the CuO2-plane mode intensity and Tc for Y1−xCaxBa2Cu3−yCoyO7−d. We suggest that this correlation as well as the CuO2-plane mode intensity offer a simple and useful probe for metal-to-insulator transition and carrier dynamics in the CuO2 plane for substituted materials. © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.Jb Electronic structure (photoemission, etc.)
74.25.F- Transport properties
74.62.Yb Other effects
74.25.Gz Optical properties
74.25.Kc Phonons
74.10.+v Occurrence, potential candidates
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions

High-Curie-temperature Ga1−xMnxAs obtained by resistance-monitored annealing

K. W. Edmonds, K. Y. Wang, R. P. Campion, A. C. Neumann, N. R. S. Farley, B. L. Gallagher, and C. T. Foxon

Appl. Phys. Lett. 81, 4991 (2002); http://dx.doi.org/10.1063/1.1529079 (3 pages) | Cited 18 times

Online Publication Date: 17 December 2002

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We show that by annealing Ga1−xMnxAs thin films at temperatures significantly lower than in previous studies, and monitoring the resistivity during growth, an unprecedented high Curie temperature TC and conductivity can be obtained. TC is unambiguously determined to be 118 K for Mn concentration x = 0.05, 140 K for x = 0.06, and 120 K for x = 0.08. We also identify a clear correlation between TC and the room temperature conductivity. The results indicate that Curie temperatures significantly in excess of the current values are achievable with improvements in growth and post-growth annealing conditions. © 2002 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.61.Ey III-V semiconductors
72.80.Ey III-V and II-VI semiconductors

Effect of underlayers of laser-assisted magnetic recording media on high-density recording

Hiroyuki Katayama, Kosuke Watanabe, Kazuhisa Takayama, Jun-ichi Sato, Shintaro Miyanishi, Kunio Kojima, and Kenji Ohta

Appl. Phys. Lett. 81, 4994 (2002); http://dx.doi.org/10.1063/1.1530746 (3 pages) | Cited 4 times

Online Publication Date: 17 December 2002

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The effect of underlayers of laser-assisted magnetic recording media has been investigated from the view point of high-density magnetic recording. The frequency response of a carrier-to-noise ratio (C/N) was measured in the media with various kinds of underlayers. It was found that they affect the high-frequency recording capability; the C/N at higher frequencies has been drastically improved for an Al-underlayered recording medium and a C/N of 40 dB was obtained at a recording frequency of 45 MHz and a track width of 0.35 μm. These results are explained by the surface morphology of the underlayer and its pinning effect on the domain-wall motion that is considered to work well for recording smaller stable domains. © 2002 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Ss Magnetic recording materials
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
68.47.De Metallic surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)

Magnetization reversal measurements in Gd/Fe multilayer antidot arrays by vector magnetometry using x-ray magnetic circular dichroism

D. R. Lee, Y. Choi, C.-Y. You, J. C. Lang, D. Haskel, G. Srajer, V. Metlushko, B. Ilic, and S. D. Bader

Appl. Phys. Lett. 81, 4997 (2002); http://dx.doi.org/10.1063/1.1532552 (3 pages) | Cited 12 times

Online Publication Date: 17 December 2002

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Fe K-edge x-ray magnetic circular dichroism (XMCD) was used as vector magnetometry to measure the magnetization rotation while field cycling Gd/Fe multilayer antidot arrays through a hysteresis loop. The measured XMCD hysteresis curves were then compared quantitatively with micromagnetic calculations to reconstruct the microscopic magnetization configurations. The best fit reveals the existence of three types of characteristic domains: two that rotate coherently during magnetization reversal and one that is strongly pinned. The behavior is explained by a simple three-domain energy model, including a phenomenological ansatz for a shape-induced demagnetization energy contribution. © 2002 American Institute of Physics.
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75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
78.66.Bz Metals and metallic alloys
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Melt-textured YBa2Cu3O7 based material doped with Li and Zn: Comparison of high trapped fields and pinning

L. Shlyk, G. Krabbes, G. Fuchs, K. Nenkov, and P. Verges

Appl. Phys. Lett. 81, 5000 (2002); http://dx.doi.org/10.1063/1.1532530 (3 pages) | Cited 16 times

Online Publication Date: 17 December 2002

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The pinning forces and trapped fields obtained in bulk YBa2Cu3O7 (YBCO)-based material doped with Li are compared with results reported for melt-processed samples doped with Zn. The increase of the volume pinning force of Li doped material is twice that of Zn doped YBCO at 77 K. This leads to 20% higher magnetic fields trapped in the Li-doped sample at 77 K. © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors

Highly aligned, spin polarized thin films of Sr2FeMoO6 by a chemical vapor process

J. Rager, A. V. Berenov, L. F. Cohen, W. R. Branford, Y. V. Bugoslavsky, Y. Miyoshi, M. Ardakani, and J. L. MacManus-Driscoll

Appl. Phys. Lett. 81, 5003 (2002); http://dx.doi.org/10.1063/1.1532752 (3 pages) | Cited 17 times

Online Publication Date: 17 December 2002

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Highly oriented films of Sr2FeMoO6 were fabricated by ultrasonic spray pyrolysis. A combined organic/inorganic solution was developed and the films were deposited on single-crystal LaAlO3 between 600 °C and 900 °C followed by postannealing at 850 °C or 1200 °C in Ar/5% H2. Optimum films showed a metallic resistivity behavior with less than a 0.25% magnetoresistive effect at 50 K, 1 T, indicative of highly quality intra- and intergranular material. At 4.2 K, the lower bound saturation magnetization, Ms was ∼ 2.5 μB/f.u. and the transport spin polarization was 60±3%. © 2002 American Institute of Physics.
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72.25.Ba Spin polarized transport in metals
81.15.Rs Spray coating techniques
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.At Metal and metallic alloys
71.30.+h Metal-insulator transitions and other electronic transitions
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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