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14 Aug 2006

Volume 89, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 89, 073501 (2006); http://dx.doi.org/10.1063/1.2335838 (3 pages)

Ingrid Graz, Martin Kaltenbrunner, Christoph Keplinger, Reinhard Schwödiauer, Siegfried Bauer, Stéphanie P. Lacour, and Sigurd Wagner
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ac susceptibility and critical-current densities in sintered YBa2Cu3O7−δ superconductors

D.-X. Chen, E. Pardo, A. Sanchez, and E. Bartolomé

Appl. Phys. Lett. 89, 072501 (2006); http://dx.doi.org/10.1063/1.2336596 (3 pages) | Cited 11 times

Online Publication Date: 14 August 2006

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The field-amplitude and frequency dependent complex ac susceptibility of a well sintered YBa2Cu3O7−δ disk has been measured at 77 K, which shows that its intra- and intergranular critical-current densities are determined by the collective flux creep inside the grains and the maximum Josephson currents across the grain boundaries, respectively. While the former is widely recognized, the latter contrasts to a popular belief of a mechanism of Josephson-vortex pinning and creep.
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74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.50.+r Tunneling phenomena; Josephson effects
61.72.Mm Grain and twin boundaries

Magnetic coupling in the mixture of different doped colossal magnetoresistances

Shih-Jye Sun, Chen-Hung Lin, Po-Yu Liao, and Hsiung Chou

Appl. Phys. Lett. 89, 072502 (2006); http://dx.doi.org/10.1063/1.2336724 (3 pages) | Cited 3 times

Online Publication Date: 14 August 2006

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Uniform bulk mixtures of micron-sized La0.7Ce0.3MnO3 and La0.7Ca0.3MnO3 colossal magnetoresistance materials have been made by standard solid-state reaction. According to the x-ray diffraction and the energy dispersion spectrum, La0.9Ce0.3MnO3 is composed of (La1−εCeε)yMnO3+δ, CeO2, and Mn–O compounds, where (La1−εCeε)yMnO3+δ behaves as a ferromagnetic material and shows no atomic interdiffusion with La0.7Ca0.3MnO3. The temperature characteristics of magnetization measurement show that the canted antiferromagnetic interaction occurs at low temperatures. The dependence of these antiferromagnetic transition temperatures on the mixing ratio can be described by the molecular mean field theory, and this reveals the strength of magnetic couplings between magnetic grains.
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75.47.Lx Magnetic oxides
75.47.Gk Colossal magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Self-synchronization in distributed Josephson junction arrays studied using harmonic analysis and power balance

J. Hassel, L. Grönberg, P. Helistö, and H. Seppä

Appl. Phys. Lett. 89, 072503 (2006); http://dx.doi.org/10.1063/1.2337536 (3 pages) | Cited 8 times

Online Publication Date: 16 August 2006

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Power generation and synchronization in Josephson junction arrays have attracted attention for a long time stemming both from fundamental interest and from application potential. The authors study the array of junctions coupled to a distributed transmission line either driven by an external microwave signal or in a self-oscillating mode. The authors simplify the theoretical treatment in terms of harmonic analysis and power balance. The model explains large operation margins of superconductor-normal-superconductor and superconductor-insulator-normal-insulator-superconductor junction arrays. The authors also compare theory, experiments, and simulations of self-oscillating externally shunted superconductor-insulator-superconductor junction arrays.
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85.25.Cp Josephson devices

Magnetization depth dependence in exchange biased thin films

R. Morales, Zhi-Pan Li, O. Petracic, X. Batlle, Ivan K. Schuller, Justin Olamit, and Kai Liu

Appl. Phys. Lett. 89, 072504 (2006); http://dx.doi.org/10.1063/1.2336742 (3 pages) | Cited 10 times

Online Publication Date: 17 August 2006

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The depth dependence of the magnetization has been studied in antiferromagnet/ferromagnet (AF/FM) exchange coupled systems. Results from vector magnetometry and magneto-optical Kerr effect probing both the AF/FM and FM/air interfaces demonstrate the existence of a magnetization depth profile in FeF2/FM (FM = Fe, Ni, and Py) bilayers, contrary to the assumptions of most exchange bias models. The appearance of asymmetrical hysteresis loops below the AF Néel temperature (TN) is explained by the creation of spring-like walls parallel to the AF/FM interface and the existence of incomplete domain walls. Changes in the reversal mechanism above TN have also been discussed.
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75.30.Et Exchange and superexchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Remanent electrical spin injection from Fe into AlGaAs/GaAs light emitting diodes

O. M. J. van ’t Erve, G. Kioseoglou, A. T. Hanbicki, C. H. Li, and B. T. Jonker

Appl. Phys. Lett. 89, 072505 (2006); http://dx.doi.org/10.1063/1.2337161 (3 pages) | Cited 10 times

Online Publication Date: 17 August 2006

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We compare surface and edge emission electroluminescence of spin-polarized light emitting diodes with Fe contacts. The edge emission geometry permits transduction of the spin state variable between the electron spin and optical polarization utilizing the in-plane remanent magnetization and low coercive fields of the metal contacts. The spin injection efficiencies are similar for electron spins oriented normal to the surface plane and in plane. The lower circular polarization consistently observed in edge emission at low magnetic fields is attributed to a partial out-of-plane orientation of the heavy hole angular momentum which persists even in wide quantum wells.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Improvement of the self-field critical current of a high-Tc superconducting tape by the edge cover from soft ferromagnetic material

F. Gömöry

Appl. Phys. Lett. 89, 072506 (2006); http://dx.doi.org/10.1063/1.2337109 (3 pages) | Cited 16 times

Online Publication Date: 18 August 2006

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Improvement of the electrical transport capability is analyzed for a superconducting wire with elliptic section, when its edges have been covered by a soft ferromagnetic material. Numerical calculations have been carried out to find the distributions of electrical current and magnetic field when reaching the critical current. The dependence of critical current density on local magnetic field and its orientation has been taken into consideration. For an arrangement that resembles a typical commercial tape from high-temperature superconductor Bi2Sr2Ca2Cu3O10 covered by a Ni sheath at edges, an increase of self-field critical current could reach 10%.
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74.72.-h Cuprate superconductors
84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
75.50.Cc Other ferromagnetic metals and alloys
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