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7 Nov 2005

Volume 87, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 87, 192502 (2005); http://dx.doi.org/10.1063/1.2128478 (3 pages)

Ki-Suk Lee, SangKook Choi, and Sang-Koog Kim
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Readout of single spins via Fano resonances in quantum point contacts

L. G. Mourokh, V. I. Puller, A. Yu. Smirnov, and J. P. Bird

Appl. Phys. Lett. 87, 192501 (2005); http://dx.doi.org/10.1063/1.2126791 (3 pages) | Cited 11 times

Online Publication Date: 31 October 2005

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We examine the feasibility of performing single-spin readout in a small quantum dot (SQD), using a quantum point contact (QPC) that is coupled to it by a larger dot with a quasicontinuous spectrum. When the Fermi energy in the QPC is approximately equal to one of the discrete levels of the SQD, a Fano resonance is observed in its conductance. We propose a procedure that uses such Fano peaks to determine the spin projection of a single electron in the SQD, in the presence of an external magnetic field that causes Zeeman splitting of its levels. We also show that this structure can exhibit Rabi oscillations when subject to microwave irradiation.
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73.23.-b Electronic transport in mesoscopic systems
73.63.Rt Nanoscale contacts
73.21.La Quantum dots
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Radiation of spin waves from magnetic vortex cores by their dynamic motion and annihilation processes

Ki-Suk Lee, SangKook Choi, and Sang-Koog Kim

Appl. Phys. Lett. 87, 192502 (2005); http://dx.doi.org/10.1063/1.2128478 (3 pages) | Cited 18 times

Online Publication Date: 1 November 2005

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We report on micromagnetic simulation results of radiation of strong spin waves from the cores of magnetic vortices driven by their dynamics motion or the annihilation of a vortex-antivortex pair in a rectangular shaped magnetic thin film. Such strong spin-waves are distinguished from spin wave modes typically excited in patterned magnetic elements. The spin wave excitation with relatively low frequencies of 0–22 GHz are associated with the shape of an element, a magnetization configuration, and an applied magnetic field, while dominating spin waves in the higher frequencies of 22–96 GHz are driven by either the motion or annihilation of vortex cores present in the confined element. The latter case yields much higher amplitudes than the former does. It is found that large torques applied at the local area of the vortex cores, driven by the large exchange fields in the core region during their dynamic motion and collapse, induce a rapid energy dissipation into the surrounding areas through the spin-wave excitation and subsequent propagation. In addition, it is found that the strong spin waves radiated by the dynamic evolution processes of the vortex cores propagate well into a long stripe-shaped magnetic wire. Such traveling spin waves can be applicable for a new generation of magnetic logic devices.
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75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High coercivity in nanocrystalline carbides Sm(Fe,Ga)9C

L. Bessais, E. Dorolti, and C. Djéga-Mariadassou

Appl. Phys. Lett. 87, 192503 (2005); http://dx.doi.org/10.1063/1.2130717 (3 pages) | Cited 1 time

Online Publication Date: 3 November 2005

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The structural and magnetic properties of metastable hexagonal SmFe9−yGayC compounds, with y = 0.25, 0.5, 0.75, and 1, have been investigated by means of powder x-ray diffraction, magnetic measurements, and high-resolution transmission electron microscopy. After carbonation, the Rietveld analysis points out an anisotropic lattice expansion more important for the carbon site. The Curie temperatures are systematically 20 to 70 K higher than those of the homologous Sm2(Fe,Ga)17 carbides. A record coercivity of 27 kOe is obtained for y = 0.25 with annealing temperature of the noncarbonated powder at 710 °C which corresponds to an optimal grain size around 28 nm. The MR/M(90 kOe) ratio of 0.57 combined with high coercivity and high TC makes this alloy suitable for permanent magnet applications.
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75.50.Vv High coercivity materials
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Ww Permanent magnets
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.40.Gh Other heat and thermomechanical treatments

Laser processed channels of easy vortex motion in YBa2Cu3O7−δ films

A. Jukna, I. Barboy, G. Jung, S. S. Banerjee, Y. Myasoedov, V. Plausinaitiene, A. Abrutis, X. Li, D. Wang, and Roman Sobolewski

Appl. Phys. Lett. 87, 192504 (2005); http://dx.doi.org/10.1063/1.2128481 (3 pages) | Cited 7 times

Online Publication Date: 4 November 2005

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Vortex dynamics in laser-patterned channels for easy motion in YBa2Cu3O7−δ thin-film bridges has been investigated by electric transport and magneto-optical measurements. It has been found that the laser-writing technique, relying on selective deoxygenation of the illuminated areas of YBa2Cu3O7−δ films, enables manufacturing of channels with the decreased field of the first penetration and pinning strength. Current-induced vortices confined in such channels move coherently within a limited temperature and bias ranges. Coherence in vortex motion was confirmed by the direct observation of self-resonant, Josephson-like current steps on the bridge current-voltage characteristics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.F- Transport properties
74.25.Gz Optical properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
42.62.-b Laser applications

SQUID magnetometer operating at 37 K based on nanobridges in epitaxial MgB2 thin films

D. Mijatovic, A. Brinkman, D. Veldhuis, H. Hilgenkamp, H. Rogalla, G. Rijnders, D. H. A. Blank, A. V. Pogrebnyakov, J. M. Redwing, S. Y. Xu, Q. Li, and X. X. Xi

Appl. Phys. Lett. 87, 192505 (2005); http://dx.doi.org/10.1063/1.2128482 (3 pages) | Cited 15 times

Online Publication Date: 4 November 2005

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Superconducting quantum interference devices (SQUIDs) and magnetometers are fabricated from nanoconstrictions in epitaxial MgB2 films. The nanobridges are contained within single-crystalline grains, resulting in clean transport, a large critical current density of 5×107 A/cm2 at 4.2 K, and stable SQUID voltage modulation up to 38.8 K. The magnetometer is realized with an inductively coupled pickup loop, giving rise to a field sensitivity of 1 pT Hz−1/2 down to 1 Hz. The device properties are governed by the two-band superconducting nature of MgB2, posing, however, no problems to a successful development of boride magnetic field sensing devices. The MgB2 zero-temperature London penetration depth is measured to be 62 nm, close to theoretical predictions.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.Ge Magnetometers for magnetic field measurements
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