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28 Mar 2005

Volume 86, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 131114 (2005); http://dx.doi.org/10.1063/1.1889243 (3 pages)

R. Chan, M. Feng, N. Holonyak, and G. Walter
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Enhanced annealing effect in an oxygen atmosphere on Ga1−xMnxAs

M. Malfait, J. Vanacken, V. V. Moshchalkov, W. Van Roy, and G. Borghs

Appl. Phys. Lett. 86, 132501 (2005); http://dx.doi.org/10.1063/1.1886912 (3 pages) | Cited 12 times

Online Publication Date: 21 March 2005

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We report on in situ resistivity measurements on Ga1−xMnxAs during post-growth annealing in different atmospheres. A drop in the resistivity is observed when the Ga1−xMnxAs is exposed to oxygen, which indicates that the passivation of Mn interstitials (MnI) at the free surface occurs through oxidation. The presence of oxygen can therefore be an important annealing condition for the optimization of Ga1−xMnxAs thin films, all the more since the oxidation appears to be limited to the sample surface. Annealing in an oxygen-free atmosphere leads to an increase in the resistivity indicating a second annealing mechanism besides the outdiffusion of MnI. According to our magnetization and Hall effect data, this mechanism reduces the amount of magnetically and electrically active Mn atoms.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.Cc Kinetics of defect formation and annealing
81.05.Dz II-VI semiconductors
73.61.Ey III-V semiconductors
81.40.Rs Electrical and magnetic properties related to treatment conditions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.35.Fx Diffusion; interface formation
81.65.Rv Passivation
81.65.Mq Oxidation
61.72.J- Point defects and defect clusters

Direct patterning of magnetic media via focusing light by microsphere arrays

Nikolay I. Polushkin

Appl. Phys. Lett. 86, 132502 (2005); http://dx.doi.org/10.1063/1.1894606 (3 pages) | Cited 5 times

Online Publication Date: 21 March 2005

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An approach to nanoscale patterning using focused laser beams by two-dimensional lattices of microspheres is presented. The arrays were positioned in a controllable way near the sample surface with submicron accuracy to find the focal plane. This technique has been applied for direct patterning of Fe–Cr layers which exhibit laser-induced modifications in magnetic properties. The obtained data indicate the occurrence of some irregularities in the patterned features. To understand: (1) The reasons for the observed irregularities and (2) how small patterned features can be obtainable, the Mie solution for the intensity of scattered light has been used.
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75.50.Bb Fe and its alloys
81.16.Rf Micro- and nanoscale pattern formation
42.62.-b Laser applications
42.15.-i Geometrical optics
78.20.Ls Magneto-optical effects

Electrical spin pumping of quantum dots at room temperature

C. H. Li, G. Kioseoglou, O. M. J. van ’t Erve, M. E. Ware, D. Gammon, R. M. Stroud, B. T. Jonker, R. Mallory, M. Yasar, and A. Petrou

Appl. Phys. Lett. 86, 132503 (2005); http://dx.doi.org/10.1063/1.1890469 (3 pages) | Cited 29 times

Online Publication Date: 22 March 2005

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We report on electrical control of the spin polarization of InAs/GaAs self-assembled quantum dots (QDs) at room temperature. This is achieved by electrical injection of spin-polarized electrons from an Fe Schottky contact. The circular polarization of the QD electroluminescence shows that a 5% electron spin polarization is obtained in the InAs QDs at 300 K, which is remarkably insensitive to temperature. This is attributed to suppression of the spin-relaxation mechanisms in the QDs due to reduced dimensionality. These results demonstrate that practical regimes of spin-based operation are clearly attainable in solid-state semiconductor devices.
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73.63.Kv Quantum dots
72.25.Dc Spin polarized transport in semiconductors
78.60.Fi Electroluminescence
72.25.Mk Spin transport through interfaces
72.25.Rb Spin relaxation and scattering
72.25.Hg Electrical injection of spin polarized carriers
72.25.Pn Current-driven spin pumping
78.67.Hc Quantum dots
73.30.+y Surface double layers, Schottky barriers, and work functions

Effect of the misalignment between the applied and internal magnetic fields on the critical currents of “tilted coated conductors”

B. Maiorov, B. J. Gibbons, S. Kreiskott, V. Matias, T. G. Holesinger, and L. Civale

Appl. Phys. Lett. 86, 132504 (2005); http://dx.doi.org/10.1063/1.1886253 (3 pages) | Cited 11 times

Online Publication Date: 22 March 2005

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We present angular-dependent measurements of the critical current density (Jc) of a YBa2Cu3O7 film grown on tilted buffered Ion-Beam-Assisted-Deposition MgO metal tapes. We compare samples with the current parallel and perpendicular to the tape’s direction. In samples with the current parallel to the tape, we observe an asymmetric angular dependence of Jc and a shift of the ab-planes maxima position with the magnetic field strength. The shift is a result of the misalignment between the applied and internal magnetic fields. The misalignment effect takes place at fields lower than 3 T at T = 75.5 K. For samples with the current perpendicular to the tape, we find an overall reduced value of Jc, the angular behavior is symmetrical, and no shift in the maxima position as a function of the magnetic field is observed. These results indicate that the effect of misalignment between the applied and internal magnetic fields must be taken into account when studying the angular dependence of Jc.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.F- Transport properties

Observation of enhanced thermal noise due to multiple Andreev reflection in ballistic InGaAs-based superconducting weak links

Tatsushi Akazaki, Hayato Nakano, Junsaku Nitta, and Hideaki Takayanagi

Appl. Phys. Lett. 86, 132505 (2005); http://dx.doi.org/10.1063/1.1897851 (3 pages) | Cited 2 times

Online Publication Date: 25 March 2005

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We have experimentally obtained clear evidence of enhanced thermal noise in a ballistic superconductor-normal metal-superconductor junction with an InGaAs-based two-dimensional electron gas (2DEG). The thermal noise was estimated from a comparison of measured current–voltage characteristics with those obtained with an extended Ambegaokar and Halperin theory. As a consequence, we have observed enhanced thermal noise that is much larger than that expected with normal reservoirs. This enhanced thermal noise can be explained by a theory that considers both the ballistic transport of the 2DEG and the thermal fluctuation in the coherent multiple Andreev reflection regime.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.50.+r Tunneling phenomena; Josephson effects
74.40.-n Fluctuation phenomena
74.25.F- Transport properties
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