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28 Jun 2004

Volume 84, Issue 26, pp. 5299-5475

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Appl. Phys. Lett. 84, 5398 (2004); http://dx.doi.org/10.1063/1.1767591 (3 pages)

E. Menard, K. J. Lee, D.-Y. Khang, R. G. Nuzzo, and J. A. Rogers
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Systematic enhancement of in-field critical current density with rare-earth ion size variance in superconducting rare-earth barium cuprate films

J. L. MacManus-Driscoll, S. R. Foltyn, Q. X. Jia, H. Wang, A. Serquis, B. Maiorov, L. Civale, Y. Lin, M. E. Hawley, M. P. Maley, and D. E. Peterson

Appl. Phys. Lett. 84, 5329 (2004); http://dx.doi.org/10.1063/1.1766394 (3 pages) | Cited 63 times

Online Publication Date: 17 June 2004

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Enhanced in-field critical current densities (Jcs) have been obtained in epitaxial superconducting (RE1,RE2) Ba2Cu3O7−x ( RE1 = rare‐earth ion 1, and RE2 = rare earth ion 2) films grown on both single crystal and buffered metallic substrates. For a constant average RE ionic radius (equal to that of yttrium), there is a systematic dependence of the in-field Jc on the RE ion size variance, with a small, but nonzero, variance being optimum. Compared to the standard YBa2Cu3O7−x composition, a factor of two improvement in Jc (75.5 K) is reproducibly observed at 0.2 T (∥c) for the composition Dy1/3Ho2/3Ba2Cu3O7−x on both single crystal and buffered-metallic substrates. Angular dependent magnetic field studies and transmission electron microscopy indicate the presence of additional pointlike random defects.
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74.25.Sv Critical currents
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
81.15.Fg Pulsed laser ablation deposition

Cryogenic magnetic field sensor based on the magnetoresistive effect in bulk Bi2212+USr2CaO6

M. Ionescu, B. Winton, T. Silver, S. X. Dou, and R. Ramer

Appl. Phys. Lett. 84, 5335 (2004); http://dx.doi.org/10.1063/1.1766398 (3 pages) | Cited 5 times

Online Publication Date: 17 June 2004

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A large magnetoresistive (MR) effect was observed in melt-textured (MT) Bi2212 in which USr2CaO6 was added in a proportion of 6 wt %. The resistivity measurements of MT Bi2212+6 wt % USr2CaO6 show high sensitivity to applied dc fields, as compared to pure Bi2212, in particular at low fields, below 3 T, and in a temperature range between 45 K and 85 K. In this temperature range, the MR effect of MT Bi2212+6 wt % USr2CaO6 is two orders of magnitude larger than the MR effect in pure Bi2212, and display a maximum that may be tuned to a particular temperature within the above range, by changing the amount of added nonsuperconducting compound. A cryogenic sensor was built and tested at 77 K in low fields. It shows a good sensitivity and small ( ∼ 1%) hysteresis of resistivity when the applied field was cycled between 0 T and 1 T.
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74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.72.-h Cuprate superconductors
07.55.-w Magnetic instruments and components
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Dip-pen nanolithography with magnetic Fe2O3 nanocrystals

Gautam Gundiah, Neena Susan John, P. John Thomas, G. U. Kulkarni, C. N. R. Rao, and S. Heun

Appl. Phys. Lett. 84, 5341 (2004); http://dx.doi.org/10.1063/1.1766399 (3 pages) | Cited 2 times

Online Publication Date: 17 June 2004

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Dip-pen nanolithography has been employed to obtain magnetic nanopatterns of γ-Fe2O3 nanocrystals on mica and silicon substrates. The chemical and magnetic nature of the patterns have been characterized employing low-energy electron microscopy, x-ray photoemission electron microscopy, and magnetic force microscopy measurements.
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81.16.Nd Micro- and nanolithography
75.50.Dd Nonmetallic ferromagnetic materials
68.37.Nq Low energy electron microscopy (LEEM)
79.60.-i Photoemission and photoelectron spectra
68.37.Rt Magnetic force microscopy (MFM)

Axial high-temperature superconducting gradiometer with a flexible flux transformer

M. Bick, K. E. Leslie, R. A. Binks, D. L. Tilbrook, S. K. H. Lam, R. Gnanarajan, J. Du, and C. P. Foley

Appl. Phys. Lett. 84, 5347 (2004); http://dx.doi.org/10.1063/1.1766401 (3 pages) | Cited 2 times

Online Publication Date: 17 June 2004

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An axial first-order gradiometer is formed by coupling the input coil of a flexible high-temperature superconducting flux transformer inductively to a directly coupled superconducting quantum interference device magnetometer. The transformer is patterned in a single-layer YBa2Cu3O7−x film on a flexible Hastelloy tape. The tape is bent such that the two outer pickup loops of the transformer are facing each other while perpendicular to the magnetometer plane resulting in a gradiometer baseline of 35 mm. A superconducting shield is mechanically adjusted to reduce the gradiometer response to uniform fields applied perpendicularly to both the magnetometer plane and the plane of the transformer pickup loops, by a factor of typically 7000.
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07.55.Ge Magnetometers for magnetic field measurements
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Inherent charge transfer layer formation at La0.6Sr0.4FeO3/La0.6Sr0.4MnO3 heterointerface

H. Kumigashira, D. Kobayashi, R. Hashimoto, A. Chikamatsu, M. Oshima, N. Nakagawa, T. Ohnishi, M. Lippmaa, H. Wadati, A. Fujimori, K. Ono, M. Kawasaki, and H. Koinuma

Appl. Phys. Lett. 84, 5353 (2004); http://dx.doi.org/10.1063/1.1766405 (3 pages) | Cited 26 times

Online Publication Date: 17 June 2004

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We have investigated the Mn 3d spectral function in La0.6Sr0.4FeO3(LSFO)/La0.6Sr0.4MnO3(LSMO) heterointerfaces as well as of La1−x SrxMnO3 films using Mn 2p−3d resonant photoemission spectroscopy. The strong enhancement of the Mn 3d spectra at the Mn 2p−3d threshold enables us to extract the Mn 3d spectra of LSMO layers in the vicinity of the interface with the LSFO overlayers. We have found that the spectral intensity of eg↑ states near the Fermi level is gradually reduced with increasing LSFO overlayer thickness and is finally saturated at 5–7 ML. The close similarity in reduction of the intensity of the eg↑ states between the LSFO/LSMO interface and hole-doped LSMO films indicates the occurrence of charge transfer at the interface between the LSMO and LSFO layers.
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79.60.Jv Interfaces; heterostructures; nanostructures
73.20.At Surface states, band structure, electron density of states
75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
71.20.Ps Other inorganic compounds
71.70.Gm Exchange interactions

Pinning phenomena in a superconducting film with a square lattice of artificial pinning centers

Z. Jiang, D. A. Dikin, V. Chandrasekhar, V. V. Metlushko, and V. V. Moshchalkov

Appl. Phys. Lett. 84, 5371 (2004); http://dx.doi.org/10.1063/1.1767278 (3 pages) | Cited 5 times

Online Publication Date: 17 June 2004

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We study the transport properties of a superconducting Nb film with a square lattice of artificial pinning centers (APCs) as a function of dc current, at a temperature close to the superconducting transition temperature of the film. We find that, at low dc currents, the differential resistance of the film shows the standard matching field anomaly, that is, the differential resistance has a local minimum at magnetic fields corresponding to an integer number of flux lines per APC. However, at higher dc currents, the differential resistance at each matching field turns to a local maximum, which is exactly opposite to the low current behavior. This effect might indicate that the flux lines in the APC system change their flow mode as the dc current is increased.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.78.-w Superconducting films and low-dimensional structures
74.25.F- Transport properties
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.62.Yb Other effects
74.10.+v Occurrence, potential candidates

Positive exchange bias in ferromagnetic La0.67Sr0.33MnO3/SrRuO3 bilayers

X. Ke, M. S. Rzchowski, L. J. Belenky, and C. B. Eom

Appl. Phys. Lett. 84, 5458 (2004); http://dx.doi.org/10.1063/1.1767955 (3 pages) | Cited 35 times

Online Publication Date: 17 June 2004

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Epitaxial La0.67Sr0.33MnO3(LSMO)/SrRuO3(SRO) ferromagnetic bilayers have been grown on (001)SrTiO3(STO) substrates by pulsed laser deposition with atomic layer control. We observe a shift in the magnetic hysteresis loop of the LSMO layer in the same direction as the applied biasing field (positive exchange bias). The effect is not present above the Curie temperature of the SRO layer (TcSRO), and its magnitude increases rapidly as the temperature is lowered below TcSRO. The direction of the shift is consistent with an antiferromagnetic exchange coupling between the ferromagnetic LSMO layer and the ferromagnetic SRO layer. We propose that atomic layer charge transfer modifies the electronic state at the interface, resulting in the observed antiferromagnetic interfacial exchange coupling.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

X-ray energy spectrum measurements by an annular superconducting tunnel junction with trapped magnetic flux quanta

M. P. Lisitskiy, C. Nappi, M. Ejrnaes, R. Cristiano, M. Huber, K. Rottler, J. Jochum, F. von Feilitzsch, and A. Barone

Appl. Phys. Lett. 84, 5464 (2004); http://dx.doi.org/10.1063/1.1766396 (3 pages) | Cited 3 times

Online Publication Date: 17 June 2004

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We report on the 55Fe x-ray pulse height spectrum of an annular superconducting tunnel junction (STJ) collected without an external magnetic field. An energy resolution of 100 eV was obtained for the Kα line of the top electrode. The Josephson critical current and Fiske resonances were suppressed by the presence of trapped magnetic flux quanta which created a persistent current and self-generated magnetic field. The obtained energy resolution and the stability of the trapped magnetic flux under irradiation demonstrate the capability of an annular STJ device with trapped flux quanta to detect radiation without using the external magnetic field that is required in the conventional detection scheme.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
85.25.Cp Josephson devices
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
29.40.Wk Solid-state detectors
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.50.+r Tunneling phenomena; Josephson effects
73.23.Ra Persistent currents
78.70.-g Interactions of particles and radiation with matter
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