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29 Oct 2007

Volume 91, Issue 18, Articles (18xxxx)

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Appl. Phys. Lett. 91, 183501 (2007); http://dx.doi.org/10.1063/1.2801554 (3 pages)

Aurelien Du Pasquier, Daniel D. T. Mastrogiovanni, Lauren A. Klein, Tong Wang, and Eric Garfunkel
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Enhancement of ferromagnetism upon thermal annealing in pure ZnO

S. Banerjee, M. Mandal, N. Gayathri, and M. Sardar

Appl. Phys. Lett. 91, 182501 (2007); http://dx.doi.org/10.1063/1.2804081 (3 pages) | Cited 66 times

Online Publication Date: 29 October 2007

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We report here the enhancement of ferromagnetism in pure ZnO upon thermal annealing with the ferromagnetic transition temperature Tc above room temperature. We observe a finite coercive field up to 300 K and a finite thermoremanent magnetization up to 340 K for the annealed sample. We propose that magnetic moments can be formed at anionic vacancy clusters. Ferromagnetism can occur due to either superexchange between vacancy clusters via isolated F+ centers or through a limited electron delocalization between vacancy clusters. Isolated vacancy clusters or isolated F+ centers give rise to a strong paramagneticlike behavior below 10 K.
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61.72.Cc Kinetics of defect formation and annealing
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.J- Point defects and defect clusters
75.50.Dd Nonmetallic ferromagnetic materials

Precessional reversal in exchange-coupled composite magnetic elements

Boris Livshitz, Akihiro Inomata, H. Neal Bertram, and Vitaliy Lomakin

Appl. Phys. Lett. 91, 182502 (2007); http://dx.doi.org/10.1063/1.2801362 (3 pages) | Cited 17 times

Online Publication Date: 29 October 2007

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Magnetization reversal in composite exchange-coupled dual-layer magnetic elements can occur in the regime of precessional reversal. Compared to the regime of damping reversal in composite elements, the regime of precessional reversal exhibits substantially reduced reversal fields with modified angular dependence. Precessional reversal in the composite elements can occur for write field rise times of more than an order larger than those in homogeneous (single-layer) elements. Such long rise times can be achieved in practical writing systems even for materials with an ultrahigh anisotropy. The identified phenomena have potential applications in high density hard drives and magnetic random access memory systems.
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75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
84.30.Sk Pulse and digital circuits
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Magnetic domain structure of a technically patterned ferromagnetic La0.6Sr0.4MnO3 thin film

M. Kubota, T. Taniuchi, R. Yasuhara, H. Kumigashira, M. Oshima, K. Ono, H. Okazaki, T. Wakita, T. Yokoya, H. Akinaga, M. Lippmaa, M. Kawasaki, and H. Koinuma

Appl. Phys. Lett. 91, 182503 (2007); http://dx.doi.org/10.1063/1.2801699 (3 pages) | Cited 5 times

Online Publication Date: 30 October 2007

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By using photoelectron emission microscopy, we systematically investigated the magnetic domain in the La0.6Sr0.4MnO3 patterned thin film with several microns, in which we can control the ratio of a shape anisotropy to a step-induced uniaxial anisotropy in magnitude. We demonstrate that a cooperative effect of a step-induced uniaxial anisotropy with a shape anisotropy causes the formation of a single domain, whereas the competitive effect makes a multimagnetic domain.
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75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Gw Magnetic anisotropy
79.60.Dp Adsorbed layers and thin films

Soft magnetism, magnetostriction, and microwave properties of FeGaB thin films

J. Lou, R. E. Insignares, Z. Cai, K. S. Ziemer, M. Liu, and N. X. Sun

Appl. Phys. Lett. 91, 182504 (2007); http://dx.doi.org/10.1063/1.2804123 (3 pages) | Cited 29 times

Online Publication Date: 31 October 2007

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A series of (Fe100−yGay)1−xBx (x = 0–21 and y = 9–17) films were deposited; their microstructure, soft magnetism, magnetostrictive behavior, and microwave properties were investigated. The addition of B changes the FeGaB films from polycrystalline to amorphous phase and leads to excellent magnetic softness with coercivity <1 Oe, high 4πMs, self-biased ferromagnetic resonance (FMR) frequency of 1.85 GHz, narrow FMR linewidth (X band) of 16–20 Oe, and a high saturation magnetostriction constant of 70 ppm. The combination of these properties makes the FeGaB films potential candidates for tunable magnetoelectric microwave devices and other rf/microwave magnetic device applications.
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75.80.+q Magnetomechanical effects, magnetostriction
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.70.Ak Magnetic properties of monolayers and thin films
81.05.Bx Metals, semimetals, and alloys

Epitaxial growth of M-type Ba-hexaferrite films on MgO (111)‖SiC (0001) with low ferromagnetic resonance linewidths

Zhaohui Chen, Aria Yang, Antone Gieler, V. G. Harris, C. Vittoria, P. R. Ohodnicki, K. Y. Goh, M. E. McHenry, Zhuhua Cai, Trevor L. Goodrich, and Katherine S. Ziemer

Appl. Phys. Lett. 91, 182505 (2007); http://dx.doi.org/10.1063/1.2794011 (3 pages) | Cited 15 times

Online Publication Date: 31 October 2007

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Barium hexaferrite (BaM) films were deposited on 10 nm MgO (111) films on 6H silicon carbide (0001) substrates by pulsed laser deposition from a homogeneous BaFe12O19 target. The MgO layer, deposited by molecular beam epitaxy, alleviated lattice mismatch and interdiffusion between film and substrate. X-ray diffraction showed strong crystallographic alignment while pole figures exhibited reflections consistent with epitaxial growth. After optimized annealing, these BaM films have a perpendicular magnetic anisotropy field of 16 900 Oe, a magnetization (as 4πMs) of 4.4 kG, and a ferromagnetic resonance peak-to-peak derivative linewidth at 53 GHz of 96 Oe, thus demonstrating sufficient properties for microwave device applications.
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81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
75.30.Gw Magnetic anisotropy
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Suppression of vortex channeling in meandered YBa2Cu3O7−δ grain boundaries

J. H. Durrell, D. M. Feldmann, and C. Cantoni

Appl. Phys. Lett. 91, 182506 (2007); http://dx.doi.org/10.1063/1.2801696 (3 pages) | Cited 9 times

Online Publication Date: 31 October 2007

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We report on the in-plane magnetic field (H) dependence of the critical current density (Jc) in meandered and planar single grain boundaries (GBs) isolated in YBa2Cu3O7−δ (YBCO) coated conductors. The meandered boundaries resulted from metal-organic deposition, and the planar boundaries resulted from physical vapor deposition. The Jc(H) properties of the planar GB are consistent with those previously seen in single GBs of YBCO films grown on SrTiO3 bicrystals. In the straight boundary, a characteristic flux channeling regime when H is oriented near the GB plane, associated with a reduced Jc, is seen. The meandered GB does not show vortex channeling since it is not possible for a sufficient length of vortex line to lie within it.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Strong reduction of field-dependent microwave surface resistance in YBa2Cu3O7−δ with submicrometric BaZrO3 inclusions

N. Pompeo, R. Rogai, E. Silva, A. Augieri, V. Galluzzi, and G. Celentano

Appl. Phys. Lett. 91, 182507 (2007); http://dx.doi.org/10.1063/1.2803856 (3 pages) | Cited 12 times

Online Publication Date: 31 October 2007

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We observe a strong reduction of the field induced thin film surface resistance measured at high microwave frequency (ν = 47.7 GHz) in YBa2Cu3O7−δ thin films grown on SrTiO3 substrates, as a consequence of the introduction of submicrometric BaZrO3 particles. The field increase of the surface resistance is smaller by a factor of ∼ 3 in the film with BaZrO3 inclusions, while the zero-field properties are not much affected. Combining surface resistance and surface reactance data, we conclude (a) that BaZrO3 inclusions determine very deep and steep pinning wells and (b) that the pinning changes nature with respect to the pure film.
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74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.F- Transport properties
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