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5 Mar 2007

Volume 90, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 90, 101901 (2007); http://dx.doi.org/10.1063/1.2712772 (3 pages)

S. N. Yi, Jong H. Na, Kwan H. Lee, Anas F. Jarjour, Robert A. Taylor, Y. S. Park, T. W. Kang, S. Kim, D. H. Ha, G. Andrew, and D. Briggs
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Reversal modes in magnetic nanotubes

P. Landeros, S. Allende, J. Escrig, E. Salcedo, D. Altbir, and E. E. Vogel

Appl. Phys. Lett. 90, 102501 (2007); http://dx.doi.org/10.1063/1.2437655 (3 pages) | Cited 43 times

Online Publication Date: 5 March 2007

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The magnetic switching of ferromagnetic nanotubes is investigated as a function of their geometry. Two independent methods are used: Numerical simulations and analytical calculations. It is found that for long tubes the reversal of magnetization is achieved by two mechanisms: The propagation of a transverse domain wall or propagation of a vortex domain wall depending on the internal and external radii of the tube.
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75.75.-c Magnetic properties of nanostructures
75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
75.40.Mg Numerical simulation studies
61.46.Fg Nanotubes

Differential magnetostrictive response in magnetically annealed Tb0.36Dy0.64(Fe0.85Co0.15)2 with ⟨110⟩ crystal orientation

Tianyu Ma, Mi Yan, Jingjing Zhang, Wei Luo, Chengbao Jiang, and Huibin Xu

Appl. Phys. Lett. 90, 102502 (2007); http://dx.doi.org/10.1063/1.2472270 (3 pages) | Cited 9 times

Online Publication Date: 5 March 2007

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Magnetic heat treatment has been carried out on a giant magnetostrictive alloy Tb0.36Dy0.64(Fe0.85Co0.15)2 with ⟨110⟩ crystal orientation. A dramatic improvement in magnetostriction along and perpendicular to the crystal axis (defined as λ‖ and λ⊥, respectively) occurs when cooling the sample through the Curie temperature TC under 240 kA/m applied perpendicular to its axis. When the applied annealing field was parallel to the crystal axis, the magnetostrictive behavior becomes “anomalous;” negative λ‖ and positive λ⊥ are obtained in low fields, accompanied with relatively low values in high fields. A single-{111}-twin model has been suggested to explain such differential magnetostrictive response.
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75.80.+q Magnetomechanical effects, magnetostriction
75.60.Nt Magnetic annealing and temperature-hysteresis effects
75.50.Bb Fe and its alloys
61.50.-f Structure of bulk crystals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Lattice dynamics of the filled skutterudite CeOs4Sb12

C. P. Yang, H. Wang, K. Iwasa, M. Kohgi, H. Sugawara, and H. Sato

Appl. Phys. Lett. 90, 102503 (2007); http://dx.doi.org/10.1063/1.2454493 (3 pages) | Cited 6 times

Online Publication Date: 7 March 2007

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Inelastic neutron scattering was performed on both poly- and single-crystalline samples to study the lattice dynamics of the Ce-filled antimonide skutterudite. For powder samples, no well-defined extra phonon excitation peak, which was reported to indicate a local Einstein oscillating mode, was detected in the low-energy region of the vibrational density of states within the experimental accuracy. However, a coherent phonon was clearly observed in single crystals at different temperatures. The dispersion curves were measured along two symmetry axes[0 1 1] and [1 0 0] at room temperature and compared with theoretical calculation by Feldman et al. [Phys. Rev. B 73, 014306 (2006)] using the model of local density approximation.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Co clustering and ferromagnetism in chemical vapor deposited Ti1−xCoxO2−δ thin films

Sueng-Hee Kang, Hoa Nguyen Thi Quynh, Soon-Gil Yoon, Eui-Tae Kim, Zonghoon Lee, and Velimir Radmilovic

Appl. Phys. Lett. 90, 102504 (2007); http://dx.doi.org/10.1063/1.2711184 (3 pages) | Cited 5 times

Online Publication Date: 7 March 2007

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Stoichiometric Ti1−xCoxO2 and oxygen-deficient Ti1−xCoxO2−δ thin films were grown on Si (001) by plasma-enhanced metal-organic chemical vapor deposition and their microstructures and ferromagnetic properties were investigated. The stoichiometric film grown at 430 °C showed no discernable Co metal clustering or measurable coercive field. In contrast, oxygen-deficient films fabricated without supplying O2 contained significant Co clusters of ∼ 10–20 nm, which appeared to be the major reason for the observed room-temperature ferromagnetism. With increasing oxygen vacancies of the films, the coercive field and saturation magnetization values increased to ∼ 460 Oe and ∼ 27 emu/cm3 (1.55μB/Co atom) approached that for bulk cobalt, respectively.
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75.50.Pp Magnetic semiconductors
75.30.Hx Magnetic impurity interactions
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
64.75.-g Phase equilibria
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Enhanced flux pinning in YBa2Cu3O7 layers by the formation of nanosized BaHfO3 precipitates using the chemical deposition method

S. Engel, T. Thersleff, R. Hühne, L. Schultz, B. Holzapfel, S. Engel, T. Thersleff, L. Schultz, B. Holzapfel, and L. Schultz

Appl. Phys. Lett. 90, 102505 (2007); http://dx.doi.org/10.1063/1.2711761 (3 pages) | Cited 25 times

Online Publication Date: 7 March 2007

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Both a high critical current density and a cost-competitive, easily upscalable procedure are among the most critical requirements for coated conductors. In this work, a low-cost method based on the trifluoroacetic acid process was used to prepare nanosized BaHfO3 particles inside a YBa2Cu3O7 film matrix. The inclusions have a perovskite structure and grow epitaxially in a cube-on-cube relationship. A drastically improved pinning force density and high irreversibility fields in the YBa2Cu3O7 layers were found and are discussed in respect to the Hf doping level in the precursor solutions, which resulted in an increased nanoinclusion content.
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74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
74.25.Sv Critical currents

Role of grain boundary and grain defects on ferromagnetism in Co:ZnO films

H. S. Hsu, J. C. A. Huang, S. F. Chen, and C. P. Liu

Appl. Phys. Lett. 90, 102506 (2007); http://dx.doi.org/10.1063/1.2711763 (3 pages) | Cited 53 times

Online Publication Date: 7 March 2007

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The annealing effects on magnetism, structure, and ac transport for Co:ZnO films have been systematically investigated. The room temperature saturation magnetization (Ms) varies drastically with Ar or Ar/H2 annealing processes. By using the impedance spectra, the change in grain boundary and grain defects of these films can be analyzed. The results demonstrate that Ar annealing produces mainly the grain boundary defects which cause the enhancement of Ms. Ar/H2-annealing creates not only grain boundary defects but also the grain defects, resulting in the stronger enhancement of Ms. Ferromagnetism for Co:ZnO films is influenced by both grain boundaries and grain defects.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
61.72.Mm Grain and twin boundaries
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Noise properties of superconducting coplanar waveguide microwave resonators

Jiansong Gao, Jonas Zmuidzinas, Benjamin A. Mazin, Henry G. LeDuc, and Peter K. Day

Appl. Phys. Lett. 90, 102507 (2007); http://dx.doi.org/10.1063/1.2711770 (3 pages) | Cited 46 times

Online Publication Date: 8 March 2007

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The authors have measured noise in thin-film superconducting coplanar waveguide resonators. This noise appears entirely as phase noise, equivalent to a jitter of the resonance frequency. In contrast, amplitude fluctuations are not observed at the sensitivity of their measurement. The ratio between the noise power in the phase and amplitude directions is large, in excess of 30 dB. These results have important implications for resonant readouts of various devices such as detectors, amplifiers, and qubits. They suggest that the phase noise is due to two-level systems in dielectric materials.
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85.25.-j Superconducting devices
84.40.Az Waveguides, transmission lines, striplines

Phase relations in the Ba–Y–Cu–O films on SrTiO3 for the ex situ BaF2 process

W. Wong-Ng, I. Levin, M. Otani, M. D. Vaudin, L. P. Cook, J. Cline, R. Feenstra, and T. Holesinger

Appl. Phys. Lett. 90, 102508 (2007); http://dx.doi.org/10.1063/1.2713124 (3 pages) | Cited 3 times

Online Publication Date: 9 March 2007

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In situ x-ray diffraction was used to establish the phase relations in high-Tc superconductor Ba–Y–Cu–O films grown on SrTiO3 through the ex situ BaF2 process. These relations differ from bulk equilibrium phase assemblages in the BaO–Y2O3–CuOx system. In particular, BaY2CuO5 (the “green phase”), a common impurity phase in bulk processing, is absent in the films. Because of the absence of this green phase, the compositional stability field of Ba2YCu3O6+x expands considerably as compared to that of the bulk system, resulting in the tie lines Ba2YCu3O6+x–Y2O3 and Ba2YCu3O6+x–Y2Cu2O5.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Dw Superconductivity phase diagrams
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