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2 Feb 2009

Volume 94, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 94, 059901 (2009); http://dx.doi.org/10.1063/1.3086725 (3 pages)

Yuta Tsukada, Tsuyoshi Honma, and Takayuki Komatsu
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Multibits magnetic recording using a ferromagnetic element with shifted vortex core position

Hong-Guang Piao, Dede Djuhana, Suhk-Kun Oh, Seong-Cho Yu, and Dong-Hyun Kim

Appl. Phys. Lett. 94, 052501 (2009); http://dx.doi.org/10.1063/1.3077024 (3 pages) | Cited 3 times

Online Publication Date: 3 February 2009

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We suggest a patterned ferromagnetic multibits element for an ultrahigh density magnetic recording media. The pattern is composed of a circular ferromagnetic disk in contact to four needle-shaped sharp equilateral triangles. By using micromagnetic simulation, we found that a spin configuration of circular ferromagnetic disk is modified with position of magnetic vortex core shifted from the center by selecting a specific combination of spin states of four needles. We explore the possibility of multibits recording by shifting magnetic vortex core position in the ferromagnetic element.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Coercivity of ledge-type L10-FePt/Fe nanocomposites with perpendicular magnetization

D. Goll and A. Breitling

Appl. Phys. Lett. 94, 052502 (2009); http://dx.doi.org/10.1063/1.3078286 (3 pages) | Cited 27 times

Online Publication Date: 3 February 2009

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Exchange-coupled ledge-type L10-FePt/Fe composite systems with out-of-plane anisotropy composed of nanostructured L10-FePt films covered by Fe are prepared to analyze the influence of the soft magnetic layer thickness on the magnetic properties. By the soft magnetic layer thickness dFe the coercivity can be tailored according to a 1/dFe1.38 relation. This result can be used to realize recording media with coercivities in the range which are afforded by conventional write heads.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.75.-c Magnetic properties of nanostructures
75.50.Ss Magnetic recording materials
75.30.Gw Magnetic anisotropy

Balancing interlayer dipolar interactions in multilevel patterned media with out-of-plane magnetic anisotropy

V. Baltz, B. Rodmacq, A. Bollero, J. Ferré, S. Landis, and B. Dieny

Appl. Phys. Lett. 94, 052503 (2009); http://dx.doi.org/10.1063/1.3078523 (3 pages) | Cited 9 times

Online Publication Date: 4 February 2009

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Nanostructures consisting of a stack of two magnetic multilayers with out-of-plane anisotropy and distinct coercivities hold great promises in spintronics devices. Yet their miniaturization leads to interlayer dipolar coupling, which results in detrimental asymmetrical behaviors of magnetization reversal or even in the loss of intermediate antiparallel configuration. In this letter, we take advantage of Ruderman–Kittel–Kasuya–Yosida interactions in order to compensate for this coupling and restore symmetry. The study has been performed on an array of square dots of 200 nm lateral size, each dot consisting of two [Co/Pt] multilayers antiferromagnetically coupled through a thin Ru spacer.
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75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ss Magnetic recording materials
75.30.Et Exchange and superexchange interactions

Interfacial defects controlled electrical and magnetotransport in Co/ZnO nanocomposites

C. Y. Hsu, J. C. A. Huang, Y. H. Lee, S. F. Chen, C. P. Liu, S. J. Sun, and Yonhua Tzeng

Appl. Phys. Lett. 94, 052504 (2009); http://dx.doi.org/10.1063/1.3077312 (3 pages) | Cited 2 times

Online Publication Date: 6 February 2009

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This work demonstrates, by frequency-dependent electrical measurements, significant variation associated with interfacial defects in Co/ZnO nanocomposites (NCs) for electrical and magnetic transport. Radio-frequency impedance measurements showed that heat treatment in an ultrahigh vacuum (UHV) increased interfacial defect density. Interfacial defects-assisted transport reduced the magnetoresistance (MR) ratio from 5.04% for the as-grown sample to 0.17% following heat treatment in UHV. The evolution of the onset frequency of power-law dispersion conductivity revealed that the increase in the interfacial defect density in Co/ZnO NCs upon heat treatment was consistent with the change in MR.
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72.20.My Galvanomagnetic and other magnetotransport effects

Local thermal bistability in MgB2 microwave coplanar resonators: Opposite jumpwise response to weak-link switching and to vortex avalanches

G. Ghigo, R. Gerbaldo, L. Gozzelino, F. Laviano, G. Lopardo, E. Monticone, C. Portesi, and E. Mezzetti

Appl. Phys. Lett. 94, 052505 (2009); http://dx.doi.org/10.1063/1.3079335 (3 pages) | Cited 3 times

Online Publication Date: 6 February 2009

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We report on specific nonlinear features in the response of microwave coplanar resonators obtained from magnesium diboride thin films. Different jumpwise behaviors observed in the resonance curves are found to be generated by either weak-link switching or vortex avalanches. Both mechanisms can be explained in terms of local-heating-induced thermal bistability, but they result in opposite effects, i.e., opposite signs in the abrupt variations of the quality factor and of the resonance frequency, due to the rf-current distribution. The weak-link-switching response shows promising characteristics (jumpwise signal, bistability, and hysteresis) for applications of MgB2 films in nonlinear devices.
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85.25.-j Superconducting devices
84.40.Az Waveguides, transmission lines, striplines
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