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8 Oct 2012

Volume 101, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 101, 153501 (2012); http://dx.doi.org/10.1063/1.4756693 (3 pages)

Brandon G. Cook, William R. French, and Kálmán Varga
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High temperature magnetic properties of SmCo5/α-Fe(Co) bulk nanocomposite magnets

Chuanbing Rong, Narayan Poudyal, X. B. Liu, Ying Zhang, M. J. Kramer, and J. Ping Liu

Appl. Phys. Lett. 101, 152401 (2012); http://dx.doi.org/10.1063/1.4758480 (3 pages) | Cited 2 times

Online Publication Date: 8 October 2012

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To find alternative high temperature magnets containing no heavy rare earths for power applications, SmCo5/Fe bulk nanocomposite magnets with enhanced energy density and high thermal stability have been produced by using a ball-milling plus warm-compaction route. Up to 30% of the Fe soft magnetic phase has been added to the composites with grain size <20 nm distributed homogenously in the matrix of the SmCo5 hard magnetic phase. It was observed that the microstructure does not change with temperature up to 500 °C. It is also observed that the thermal stability of bulk nanocomposite samples is closely related to bulk density. Energy products above 11 MGOe have been obtained at 300 °C in fully dense bulk SmCo5/Fe nanocomposite magnets, which is 65% higher than that of a single-phase counterpart at the same temperature.
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81.05.Bx Metals, semimetals, and alloys
81.07.Bc Nanocrystalline materials
81.20.Wk Machining, milling
75.75.-c Magnetic properties of nanostructures
75.50.Ww Permanent magnets
75.50.Tt Fine-particle systems; nanocrystalline materials

Propagation and scattering of spin waves in curved magnonic waveguides

V. S. Tkachenko, A. N. Kuchko, M. Dvornik, and V. V. Kruglyak

Appl. Phys. Lett. 101, 152402 (2012); http://dx.doi.org/10.1063/1.4757994 (5 pages) | Cited 2 times

Online Publication Date: 9 October 2012

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We report a continuous medium theory of dispersion and scattering of spin waves propagating in thin nanowire magnonic waveguides with curved regions. Assuming that the static magnetization is aligned along the waveguide, the curvature leads to a “geometrical” effective magnetic field term that is proportional to the square of the ratio of the exchange length to the radius of curvature of the waveguide. The term is small enough to favor the use of bended nanowire waveguides in planar magnonic data architectures. However, a stronger (multiple) winding (e.g., within helical structures) could enable design of magnonic waveguides with desired properties.
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75.30.Ds Spin waves
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Effect of inter-bit material on the performance of directly deposited bit patterned media

Naganivetha Thiyagarajah, Huigao Duan, Debra L. Y. Song, Mohamed Asbahi, Siang Huei Leong, Joel K. W. Yang, and Vivian Ng

Appl. Phys. Lett. 101, 152403 (2012); http://dx.doi.org/10.1063/1.4758478 (5 pages)

Online Publication Date: 9 October 2012

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We evaluated the effects of inter-bit material on the switching performance of bit patterned media (BPM) fabricated by direct deposition of magnetic material onto pre-patterned substrates. We performed a controlled experiment to vary the sidewall thickness and symmetry in bits with nominally identical size and pitch. Thick, asymmetric sidewalls resulted in significant broadening of the switching field distribution to 14%–20% compared to 10%–11% for bits with thin, symmetric sidewalls. These differences were attributed to changes in the intrinsic properties and dipolar interactions as supported by micromagnetic simulations. Our results highlight the importance of controlling inter-bit material to achieve high-density BPM.
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75.30.-m Intrinsic properties of magnetically ordered materials
75.78.Cd Micromagnetic simulations
75.60.-d Domain effects, magnetization curves, and hysteresis
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Giant magnetoresistance effect in graphene with asymmetrical magnetic superlattices

Q. H. Huo, R. Z. Wang, and H. Yan

Appl. Phys. Lett. 101, 152404 (2012); http://dx.doi.org/10.1063/1.4757881 (5 pages)

Online Publication Date: 10 October 2012

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We investigate a giant magnetoresistance (MR) effect in periodic, asymmetric magnetic superlattices (MSLs) on graphene. The MR ratio shows a strong dependence on both the interval of magnetic barriers and the asymmetry degree of the structures. With the increase of the number of periods, there is only one MR peak and the drift of the position of the peak appears around a specific Fermi energy. The highest value of the maximal MR ratio can be up to 1017%. Our studies indicate that the graphene-based asymmetric MSLs structure is an ideal candidate of a giant MR device, e.g., the magnetic reading device.
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75.47.De Giant magnetoresistance
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.22.Pr Electronic structure of graphene
72.20.My Galvanomagnetic and other magnetotransport effects
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Growth and ferromagnetic resonance properties of nanometer-thick yttrium iron garnet films

Yiyan Sun, Young-Yeal Song, Houchen Chang, Michael Kabatek, Michael Jantz, William Schneider, Mingzhong Wu, Helmut Schultheiss, and Axel Hoffmann

Appl. Phys. Lett. 101, 152405 (2012); http://dx.doi.org/10.1063/1.4759039 (5 pages) | Cited 1 time

Online Publication Date: 11 October 2012

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Growth of nm-thick yttrium iron garnet films and ferromagnetic resonance (FMR) linewidth properties in the films are reported. The films were grown on gadolinium gallium garnet substrates by pulsed laser deposition (PLD). Films in the 5–35 nm thickness range showed a (111) orientation and a surface roughness between 0.1 and 0.3 nm. The 10 nm films showed a 10 GHz FMR linewidth of about 6 Oe and a damping constant of 3.2 × 10−4. The FMR linewidth increases with both the surface roughness and the surface Fe deficiency. Thicker films exhibit a smaller FMR linewidth and a lower damping constant.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
81.15.Fg Pulsed laser ablation deposition
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Cc Other ferromagnetic metals and alloys
68.55.A- Nucleation and growth

Helical domain walls in constricted cylindrical NiFe nanowires

M. Chandra Sekhar, H. F. Liew, I. Purnama, W. S. Lew, M. Tran, and G. C. Han

Appl. Phys. Lett. 101, 152406 (2012); http://dx.doi.org/10.1063/1.4758469 (5 pages) | Cited 2 times

Online Publication Date: 11 October 2012

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Reducing the magnetic shape anisotropy of a cylindrical NiFe nanowire allows the formation of two vortices with opposite chirality at the two ends. At relatively low aspect ratio these two vortices are connected via a gradual rotation of the magnetization over a short region, which forms a three-dimensional helical domain wall. Micromagnetic simulations reveal that it is possible to control the number of helical domain walls in the cylindrical nanowire by geometrical constrictions engineering. A technique to create constricted Ni95Fe5/Ni87Fe13 multilayered nanowires is demonstrated, and magnetic force microscopy imaging was carried out to confirm the prediction of simulated helical domain walls.
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75.60.Ch Domain walls and domain structure
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures
75.78.Cd Micromagnetic simulations
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials

Observation of spin dependent photocoductivity in InSb quantum well nanowires

Juerong Li, A. M. Gilbertson, K. L. Litvinenko, L. F. Cohen, and S. K. Clowes

Appl. Phys. Lett. 101, 152407 (2012); http://dx.doi.org/10.1063/1.4760223 (4 pages)

Online Publication Date: 12 October 2012

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We report on the electrical detection of spin dependent photoconductivity in 500 nm wide InSb quantum well nanowires using the optical orientation of electron spins. By applying weak magnetic fields ( ≈ 200 mT), we observe a spin filtering effect of classical origin caused by spin dependent back scattering of electrons from the sidewalls. Spin dependent features in the longitudinal photovoltage decay with temperature and disappears at characteristic energy ( ≈ 50 K) consistent with the theoretical spin splitting and the thermal level broadening. We show that the observed signal is due to the inversion asymmetry of the quantum well, with an additional Zeeman contribution.
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72.40.+w Photoconduction and photovoltaic effects
73.63.Hs Quantum wells
78.67.De Quantum wells
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