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21 Jul 2008

Volume 93, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 93, 031101 (2008); http://dx.doi.org/10.1063/1.2959092 (3 pages)

Di Xu, Kevin P. Chen, Kris Ohlinger, and Yuankun Lin
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Piezoelectric disks used as metamaterial inclusions

O. Acher, M. Ledieu, A. Bardaine, and F. Levassort

Appl. Phys. Lett. 93, 032501 (2008); http://dx.doi.org/10.1063/1.2961005 (3 pages) | Cited 2 times

Online Publication Date: 21 July 2008

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The permeability of inclusions consisting of commercially available piezoelectric disks was investigated, leading to the observation of several resonances in the 100 MHz–3 GHz range. This could be described through a simple analytical relation, and the inclusions were deemed attractive for manufacturing metamaterials with negative permeabilities over a significant frequency range. Moreover, they can be used as reference permeability samples.
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77.65.-j Piezoelectricity and electromechanical effects
84.40.-x Radiowave and microwave (including millimeter wave) technology
77.22.Ch Permittivity (dielectric function)

Effect of magnetic field on domain-wall structures in two antiferromagnetically coupled Co/Pt multilayers

Z. Y. Liu, N. Li, F. Zhang, B. Xu, J. L. He, D. L. Yu, Y. J. Tian, and G. H. Yu

Appl. Phys. Lett. 93, 032502 (2008); http://dx.doi.org/10.1063/1.2962990 (3 pages) | Cited 6 times

Online Publication Date: 23 July 2008

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In antiferromagnetically coupled [Pt (5 Å)/Co (4 Å)]4/NiO (11 Å)/[Co (4 Å)/Pt (5 Å)]4 multilayer with perpendicular anisotropy, net ferromagnetic stripes are created in demagnetized state between the relatively shifted domain walls in the two Co/Pt multilayers owing to the competition between magnetostatic and exchange energies. With an external field applied antiparallel to the wall magnetization, involvement of Zeeman energy of net ferromagnetic stripes in the competition makes the net ferromagnetic stripes shrink, and the stripe width varies with field in an inversely proportional way in the low field range.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Critical fields and anisotropy of NdFeAsO0.82F0.18 single crystals

Ying Jia, Peng Cheng, Lei Fang, Huiqian Luo, Huan Yang, Cong Ren, Lei Shan, Changzhi Gu, and Hai-Hu Wen

Appl. Phys. Lett. 93, 032503 (2008); http://dx.doi.org/10.1063/1.2963361 (3 pages) | Cited 73 times

Online Publication Date: 23 July 2008

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By using flux method, we have grown single crystals of NdFeAsO0.82F0.18 at ambient pressures. Resistive measurements reveal a surprising discovery that the anisotropy Γ = (mc/mab)1/2 is below 5, which is much smaller than the theoretically calculated value. The data measured up to 400 K show a curved feature, which prevents a conjectured linear behavior for an unconventional metal. The upper critical fields determined based on the Werthamer–Helfand–Hohenberg formula [ N. R. Werthamer et al., Phys. Rev. 147, 295 (1966) ] are Hc2ab(T = 0 K) ≈  304 T and Hc2c(T = 0 K) ≈ 62–70 T. These high values indicate very encouraging applications of the new superconductors.
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74.10.+v Occurrence, potential candidates
74.70.-b Superconducting materials other than cuprates
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena

Ultrafast optical control of coercivity in GaMnAs

K. C. Hall, J. P. Zahn, A. Gamouras, S. March, J. L. Robb, X. Liu, and J. K. Furdyna

Appl. Phys. Lett. 93, 032504 (2008); http://dx.doi.org/10.1063/1.2963972 (3 pages) | Cited 10 times

Online Publication Date: 24 July 2008

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Femtosecond optical control of the magnetization and coercive field is demonstrated in GaMnAs using time-resolved magneto-optical Kerr effect techniques. These experiments reveal a near-complete, subpicosecond collapse of the hysteresis loop, consistent with femtosecond demagnetization. On longer time scales ( ∼ 300 ps) an increase in coercivity is observed, attributed to hole-mediated enhancement of the domain wall energy.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
78.47.D- Time resolved spectroscopy (>1 psec)
75.50.Pp Magnetic semiconductors
78.20.Ls Magneto-optical effects

Direct chemical synthesis of high coercivity air-stable SmCo nanoblades

C. N. Chinnasamy, J. Y. Huang, L. H. Lewis, B. Latha, C. Vittoria, and V. G. Harris

Appl. Phys. Lett. 93, 032505 (2008); http://dx.doi.org/10.1063/1.2963034 (3 pages) | Cited 19 times

Online Publication Date: 25 July 2008

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Ferromagnetic air-stable SmCo nanoparticles have been produced directly using a one-step chemical synthesis method. X-ray diffraction studies confirmed the formation of hexagonal SmCo5 as a dominant phase. High resolution transmission electron microscopy confirms the presence of uniform, anisotropic bladelike nanoparticles approximately 10 nm in width and 100 nm in length. Values of the intrinsic coercivity and the magnetization in the as-synthesized particles are 6.1 kOe and 40 emu/g at room temperature and 8.5 kOe and 44 emu/g at 10 K, respectively. This direct synthesis process is environmentally friendly and is readily scalable to large volume synthesis to meet the needs for the myriad of advanced permanent magnet applications.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Vv High coercivity materials
75.50.Ww Permanent magnets
75.50.Cc Other ferromagnetic metals and alloys
61.66.Dk Alloys

Granular L10 FePt:TiO2 (001) nanocomposite thin films with 5 nm grains for high density magnetic recording

Y. F. Ding, J. S. Chen, B. C. Lim, J. F. Hu, B. Liu, and G. Ju

Appl. Phys. Lett. 93, 032506 (2008); http://dx.doi.org/10.1063/1.2953173 (3 pages) | Cited 20 times

Online Publication Date: 25 July 2008

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FePt:TiO2 (001) thin films were deposited on CrRu/MgO underlayers by dc magnetron cosputtering. The effects of TiO2 content on microstructure and magnetic properties of the epitaxial FePt (001) films were studied. Experimental results showed that even with 20 vol % TiO2 doping, FePt films could keep a (001) preferred orientation and perpendicular anisotropy. The FePt:TiO2 (001) film with 5 nm grain size, adjustable coercivity, and reduced exchange coupling was obtained by doping 20 vol % TiO2 into FePt film, showing great potential as low noise ultrahigh density perpendicular magnetic recording media.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ss Magnetic recording materials
75.30.Gw Magnetic anisotropy
81.15.Cd Deposition by sputtering
68.55.jm Texture
61.72.-y Defects and impurities in crystals; microstructure
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