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29 Nov 2010

Volume 97, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 223101 (2010); http://dx.doi.org/10.1063/1.3519844 (3 pages)

Jin-Kyu Yang, Svetlana V. Boriskina, Heeso Noh, Michael J. Rooks, Glenn S. Solomon, Luca Dal Negro, and Hui Cao
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Current induced effective magnetic field and magnetization reversal in uniaxial anisotropy (Ga,Mn)As

M. Endo, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 97, 222501 (2010); http://dx.doi.org/10.1063/1.3520514 (3 pages) | Cited 2 times

Online Publication Date: 29 November 2010

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The authors investigate the current density and temperature dependence of current induced effective magnetic field Heff through spin-orbit interaction in a ferromagnetic semiconductor Ga0.92Mn0.08As having uniaxial magnetic anisotropy. The change of the magnitude of apparent magnetic anisotropy induced by Heff that is dependent on the current direction and density is observed by transport measurements using the planar Hall effect. The authors show the 180° magnetization switching through Heff by applying pulsed current.
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75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.20.My Galvanomagnetic and other magnetotransport effects

Observation of coupled vortex gyrations by 70-ps-time- and 20-nm-space-resolved full-field magnetic transmission soft x-ray microscopy

Hyunsung Jung, Young-Sang Yu, Ki-Suk Lee, Mi-Young Im, Peter Fischer, Lars Bocklage, Andreas Vogel, Markus Bolte, Guido Meier, and Sang-Koog Kim

Appl. Phys. Lett. 97, 222502 (2010); http://dx.doi.org/10.1063/1.3517496 (3 pages) | Cited 5 times

Online Publication Date: 29 November 2010

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We employed time- and space-resolved full-field magnetic transmission soft x-ray microscopy to observe vortex-core gyrations in a pair of dipolar-coupled vortex-state Permalloy (Ni80Fe20) disks. The 70 ps temporal and 20 nm spatial resolution of the microscope enabled us to simultaneously measure vortex gyrations in both disks and to resolve the phases and amplitudes of both vortex-core positions. We observed their correlation for a specific vortex-state configuration. This work provides a robust and direct method of studying vortex gyrations in dipolar-coupled vortex oscillators.
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07.85.Tt X-ray microscopes
75.30.Cr Saturation moments and magnetic susceptibilities
85.70.-w Magnetic devices

Control of vortex chirality in regular polygonal nanomagnets using in-plane magnetic field

S. Yakata, M. Miyata, S. Nonoguchi, H. Wada, and T. Kimura

Appl. Phys. Lett. 97, 222503 (2010); http://dx.doi.org/10.1063/1.3521407 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2010

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The authors have proposed a control method of the magnetic vortex chirality in regular polygonal nanomagnets with an odd number of sides. The asymmetric nucleation energy of the vortex from the uniformly magnetized state enables us to simply control the vortex chirality by an in-plane magnetic field. The reliability of the proposed method has been numerically and experimentally confirmed in the triangle, pentagonal, heptagonal, and nonagonal Permalloy nanomagnets. The authors also confirmed that the vortex chirality is uncontrollable when the number of the side is even.
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75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities

Large enhancement of the anomalous Hall effect in Co/Pt multilayers sandwiched by MgO layers

S. L. Zhang, J. Teng, J. Y. Zhang, Y. Liu, J. W. Li, G. H. Yu, and S. G. Wang

Appl. Phys. Lett. 97, 222504 (2010); http://dx.doi.org/10.1063/1.3522653 (3 pages) | Cited 3 times

Online Publication Date: 30 November 2010

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We report a large enhanced anomalous Hall effect (AHE) in the Co/Pt multilayers sandwiched by two MgO layers. The Hall resistivity (ρxy) was over an order of magnitude larger than that in pure Co/Pt multilayers. By optimizing the thickness of MgO layers, a high field sensitivity value of 2445 V/A T for Hall sensors was achieved. The enhancement of AHE is mainly attributed to the MgO–Pt interfacial effect.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
73.63.-b Electronic transport in nanoscale materials and structures
73.40.Rw Metal-insulator-metal structures

Measurement of the attempt frequency in antiferromagnets

G. Vallejo-Fernandez, N. P. Aley, J. N. Chapman, and K. O’Grady

Appl. Phys. Lett. 97, 222505 (2010); http://dx.doi.org/10.1063/1.3522887 (3 pages)

Online Publication Date: 2 December 2010

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The characteristic relaxation frequency of a granular antiferromagnet f0 in the Néel–Arrhenius expression has been calculated from a high resolution measurement of the time dependence of the median blocking temperature of a CoFe/IrMn exchange biased system. Calculations based on a granular model give f0 = (2.1±0.4)×1012 s−1, three orders of magnitude greater than values commonly found in the literature.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics

Three-dimensional nanoscale superconducting quantum interference device pickup loops

E. J. Romans, E. J. Osley, L. Young, P. A. Warburton, and W. Li

Appl. Phys. Lett. 97, 222506 (2010); http://dx.doi.org/10.1063/1.3521262 (3 pages) | Cited 1 time

Online Publication Date: 2 December 2010

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Nanoscale superconducting quantum interference devices (SQUIDs) have sensitivities approaching that required for single-spin detection, but they only measure fields perpendicular to their plane and can be difficult to tightly couple to magnetic sources on the same chip. To remove these limitations we used focused-ion-beam-induced chemical vapor deposition to directly write a SQUID structure with three-dimensional, freestanding pickup loops using superconducting tungsten nanowires. By applying a localized field, we investigated the pickup loop response, and found that it exhibits Meissner screening corresponding to a penetration depth λ(T) consistent with BCS theory in the dirty limit and λ(0) = 330 nm.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
81.07.Gf Nanowires
74.25.Ha Magnetic properties including vortex structures and related phenomena
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Metamagnetic transitions and magnetocaloric effect in epitaxial Ni–Co–Mn–In films

R. Niemann, O. Heczko, L. Schultz, and S. Fähler

Appl. Phys. Lett. 97, 222507 (2010); http://dx.doi.org/10.1063/1.3517443 (3 pages) | Cited 2 times

Online Publication Date: 3 December 2010

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Due to their large strains and multifunctionality, magnetic shape memory alloys are of particular interest for microsystems. Here epitaxially grown metamagnetic Ni–Co–Mn–In films on MgO (001) are analyzed which exhibit a magnetically induced austenite transition. This opens the way to use Ni–Co–Mn–In films in microactuators combining high stroke with high forces. Additionally these films exhibit an inverse magnetocaloric effect with an entropy change of 8.8 J kg−1 K−1 in 9 T at 353 K. The high surface-to-volume fraction of films promises a fast heat exchange, which is beneficial for efficient magnetic cooling.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
65.40.gd Entropy

A superconducting 180° hybrid ring coupler for circuit quantum electrodynamics

E. Hoffmann, F. Deppe, T. Niemczyk, T. Wirth, E. P. Menzel, G. Wild, H. Huebl, M. Mariantoni, T. Weißl, A. Lukashenko, A. P. Zhuravel, A. V. Ustinov, A. Marx, and R. Gross

Appl. Phys. Lett. 97, 222508 (2010); http://dx.doi.org/10.1063/1.3522650 (3 pages)

Online Publication Date: 3 December 2010

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Superconducting circuit quantum electrodynamics experiments with propagating microwaves require devices acting as beam splitters. Using niobium thin films on silicon and sapphire substrates, we fabricated superconducting 180° microstrip hybrid ring couplers, acting as beam splitters with center frequencies of about 6 GHz. For the magnitude of the coupling and isolation, we find −3.5±0.5 dB and at least −15 dB, respectively, in a bandwidth of 2 GHz. We also investigate the effect of reflections at the superconductor-normal conductor contact by means of low temperature laser scanning microscopy. Our measurements show that our hybrid rings are well suited for on-chip applications in circuit quantum electrodynamics experiments.
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85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
84.40.Az Waveguides, transmission lines, striplines
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