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10 Oct 2005

Volume 87, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 87, 151103 (2005); http://dx.doi.org/10.1063/1.2089157 (3 pages)

Andrew B. Greytak, Carl J. Barrelet, Yat Li, and Charles M. Lieber
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Dendritic magnetic avalanches in carbon-free MgB2 thin films with and without a deposited Au layer

Eun-Mi Choi, Hyun-Sook Lee, Hyun Jung Kim, Byeongwon Kang, Sung-Ik Lee, A. A. F. Olsen, D. V. Shantsev, and T. H. Johansen

Appl. Phys. Lett. 87, 152501 (2005); http://dx.doi.org/10.1063/1.2084323 (3 pages) | Cited 22 times

Online Publication Date: 3 October 2005

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From magneto optic images (MOI), the dendritic magnetic avalanche is known to appear dominantly for thin films of the newly discovered MgB2. To clarify the origin of this phenomenon, we studied in detail the MOI of carbon-free MgB2 thin films with and without a deposited gold layer. The MOI indicated that carbon contamination was not the main source of the avalanche. The MOI clearly showed that the deposition of metallic gold on top of a MgB2 thin film improved its thermal stability and suppressed the sudden appearance of the dendritic flux avalanche. This is consistent with the previous observation of flux noise in the magnetization.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.78.-w Superconducting films and low-dimensional structures
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
74.25.Sv Critical currents

High-magnetic-moment core-shell-type FeCo–Au/Ag nanoparticles

Jianmin Bai and Jian-Ping Wang

Appl. Phys. Lett. 87, 152502 (2005); http://dx.doi.org/10.1063/1.2089171 (3 pages) | Cited 28 times

Online Publication Date: 4 October 2005

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We developed a physical technique combining an on-line sputtering/evaporation process with an integrated nanocluster deposition process to prepare core-shell-type nanoparticles. High-magnetic-moment (Fe60Co40)coreAushell and (Fe60Co40)coreAgshell superparamagnetic nanoparticles with controllable particle size of 10–20 nm and Au/Ag shell thickness of 1–3 nm were prepared by using this method. Au shell is not only functional for the potential biocompatibility but also the key to prevent the oxidation of FeCo nanoparticles. Saturation magnetization of (Fe60Co40)coreAushell nanoparticles was found three times higher than that of iron oxide nanoparticles. This technique enables us to control independently the dimensions of core and shell and select individually materials for core and shell for any other core-shell-type nanoparticles.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Cr Saturation moments and magnetic susceptibilities
75.20.En Metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.16.Pr Micro- and nano-oxidation

X-ray ferromagnetic resonance spectroscopy

G. Boero, S. Rusponi, P. Bencok, R. S. Popovic, H. Brune, and P. Gambardella

Appl. Phys. Lett. 87, 152503 (2005); http://dx.doi.org/10.1063/1.2089180 (3 pages) | Cited 16 times

Online Publication Date: 5 October 2005

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We present a method to measure continuous-wave ferromagnetic resonance (FMR) spectra based on the core-level absorption of circularly polarized x rays. The technique is demonstrated by using a monochromatic x-ray beam incident on an yttrium–iron–garnet sample excited by a microwave field at 2.47 GHz. FMR spectra are obtained by monitoring the x-ray absorption intensity at the photon energy corresponding to the maximum of the magnetic circular dichroism effect at the iron L2,3 edges as a function of applied magnetic field. The x-ray FMR signal is shown to be energy dependent, which makes the technique element sensitive and opens up new possibilities to perform element-resolved FMR in magnetic alloys and multilayers.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
07.85.Nc X-ray and γ-ray spectrometers
75.50.Gg Ferrimagnetics
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
78.70.Dm X-ray absorption spectra
75.50.Dd Nonmetallic ferromagnetic materials
73.20.At Surface states, band structure, electron density of states
78.20.Ls Magneto-optical effects

Current-induced asymmetric transport in La0.8Ca0.2MnO3 epitaxial thin films

F. X. Hu and J. Gao

Appl. Phys. Lett. 87, 152504 (2005); http://dx.doi.org/10.1063/1.2093934 (3 pages) | Cited 14 times

Online Publication Date: 5 October 2005

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We investigated the influence of a dc current on the transport properties in La0.8Ca0.2MnO3 epitaxial thin films grown on SrTiO3 substrates. A prominent finding is the appearance of asymmetric transport properties, like the behavior of p-n junctions, in a wide temperature range from 10 K to 300 K after the films were applied by a dc current over a threshold value. The asymmetric behavior resulted from a relative weak excitation is unstable and even spontaneously disappears. By optimizing excitation condition, the rectifyinglike behavior turns to be more significant and stable. Applying a small ac current could make the asymmetric transport collapse, subsequently, conventional symmetric transport behaviors appear. Phase separation and the coexistent ferromagnetic phases with different orbital order are taken into account in the interpretation of the observed phenomena.
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75.47.Lx Magnetic oxides
75.47.Gk Colossal magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
71.27.+a Strongly correlated electron systems; heavy fermions
75.70.Ak Magnetic properties of monolayers and thin films

Large induced magnetic anisotropy in manganese spinel ferrite films

Xu Zuo, Aria Yang, Soack-Dae Yoon, Joseph A. Christodoulides, Vincent G. Harris, and Carmine Vittoria

Appl. Phys. Lett. 87, 152505 (2005); http://dx.doi.org/10.1063/1.2084341 (3 pages) | Cited 17 times

Online Publication Date: 7 October 2005

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The oxygen pressure dependence of magnetic anisotropy in pulse laser deposited manganese ferrite (MnFe2O4) films was investigated. Magnetic anisotropy fields (Ha) are shown to exceed 5 kOe when films were processed at oxygen pressures below 5 mTorr. Further, it is shown that the magnetically preferred direction of Ha can be aligned either along the film plane (pO2<8 mTorr) or perpendicular to it (pO2>8 mTorr). The ability to induce large perpendicular magnetic anisotropy in spinel ferrites allows for new applications (i.e., phase shifters, filters, isolators, and circulators) near or above X-band frequencies to be considered.
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75.30.Gw Magnetic anisotropy
75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
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