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24 Dec 2007

Volume 91, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 91, 261106 (2007); http://dx.doi.org/10.1063/1.2825578 (3 pages)

W. M. Zhu, T. Zhong, A. Q. Liu, X. M. Zhang, and M. Yu
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Improvement in electric and dielectric properties of nanoferrite synthesized via reverse micelle technique

Sangeeta Thakur, S. C. Katyal, and M. Singh

Appl. Phys. Lett. 91, 262501 (2007); http://dx.doi.org/10.1063/1.2824454 (3 pages) | Cited 11 times

Online Publication Date: 26 December 2007

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Nano nickel zinc ferrite (Ni0.58Zn0.42Fe2O4) with fascinating dielectric properties which reveal a direction for application was synthesized by reverse micelle technique. Dielectric constant and dielectric losses are controlled up to a measurement temperature of around 473 K at higher frequency range of 9–19 MHz. The dielectric loss of the sample investigated at room temperature is only 0.003 at 19 MHz. The presently studied nanoferrite also exhibits a high value of dc resistivity, 108 Ω cm. High resistivity and low dielectric constant and loss can be corelated to small grain size and better compositional stoichiometry obtained as a result of processing via reverse micelle technique at low sintering temperature (773 K).
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73.63.Bd Nanocrystalline materials
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

X-ray absorption spectroscopy and x-ray magnetic circular dichroism of epitaxially grown Heusler alloy Co2MnSi ultrathin films facing a MgO barrier

Toshiaki Saito, Toshikazu Katayama, Takayuki Ishikawa, Masafumi Yamamoto, Daisuke Asakura, and Tsuneharu Koide

Appl. Phys. Lett. 91, 262502 (2007); http://dx.doi.org/10.1063/1.2824856 (3 pages) | Cited 10 times

Online Publication Date: 26 December 2007

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We element specifically studied the electronic and magnetic states of epitaxially grown full-Heusler alloy Co2MnSi (CMS) 1.1 nm (4 ML) thick ultrathin films facing an epitaxial MgO(001) tunnel barrier by means of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). In situ reflection high-energy electron-diffraction observations indicated that the CMS films grew into the L21 structure. The observed XAS and XMCD spectra revealed that the CMS ultrathin film was not oxidized. The ratio of Mn and Co spin magnetic moments obtained by applying the sum rules was about 2.7, close to a theoretical value of 2.8 for CMS with the L21 structure.
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75.70.Ak Magnetic properties of monolayers and thin films
78.70.Dm X-ray absorption spectra
75.30.Cr Saturation moments and magnetic susceptibilities
73.20.At Surface states, band structure, electron density of states

Tuning the crystal structure and magnetic properties of Fe doped In2O3 nanocrystals

Dewei Chu, Yu-Ping Zeng, Dongliang Jiang, and Zhongming Ren

Appl. Phys. Lett. 91, 262503 (2007); http://dx.doi.org/10.1063/1.2815661 (3 pages) | Cited 13 times

Online Publication Date: 26 December 2007

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Fe doped In2O3 nanocrystals were synthesized by a coprecipitation method under external magnetic fields. X-ray diffraction data and high-resolution transmission electron microscopy analyses indicated the formation of single phase without any parasitic phases. The crystal structure of the nanocrystals is tuned by changing Fe concentrations and intensities of magnetic fields. Room temperature ferromagnetism in Fe doped In2O3 nanocrystals can be activated by suitable magnetic fields.
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61.46.Hk Nanocrystals
61.66.Fn Inorganic compounds
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing

Electrical spin injection into the InAs/GaAs wetting layer

C. H. Li, G. Kioseoglou, A. T. Hanbicki, R. Goswami, C. S. Hellberg, B. T. Jonker, M. Yasar, and A. Petrou

Appl. Phys. Lett. 91, 262504 (2007); http://dx.doi.org/10.1063/1.2827585 (3 pages) | Cited 4 times

Online Publication Date: 26 December 2007

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We have used transport measurements, transmission electron microscopy, and polarization dependent photo- and electroluminescence to characterize the InAs/GaAs(001) wetting layer (WL) system. Transport data confirm formation of a two-dimensional electron gas in modulation-doped structures. The optical pumping of the WL in an undoped structure provides a ratio of radiative to spin lifetime (τr/τs) ∼ 1, which is constant over the measurement range of 10–100 K. We demonstrate efficient spin injection from an Fe Schottky tunnel contact into the WL, and achieve an electron spin polarization of ∼ 55% from 5 to 50 K, which decreases monotonically with increasing temperature.
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73.40.Ns Metal-nonmetal contacts
72.25.Dc Spin polarized transport in semiconductors
72.25.Mk Spin transport through interfaces
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.60.Fi Electroluminescence
78.55.Cr III-V semiconductors

Exchange bias in self-organized Nd0.5Sr0.5MnO3 bilayer film

Y. H. Hyun, S. Y. Park, Y. P. Lee, V. G. Prokhorov, and V. L. Svetchnikov

Appl. Phys. Lett. 91, 262505 (2007); http://dx.doi.org/10.1063/1.2825418 (3 pages) | Cited 4 times

Online Publication Date: 26 December 2007

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The self-organized Nd0.5Sr0.5MnO3 bilayer film with a homogeneous chemical composition and different microstructures has been prepared by rf-magnetron sputtering. The top layer of the film has a columnlike nanostructure while the bottom one forms an epitaxial crystal structure. The magnetic properties of the film mimic the behavior of superparamagnetic particles grown onto the ferromagnetic layer. An exchange-bias effect was observed at a temperature below the blocking one, even in the present ferromagnetic hybrid system.
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75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films

A universal relation between resistivity and magnetization in paramagnetic state of manganites

J. Z. Wang, J. R. Sun, G. J. Liu, F. X. Hu, T. Y. Zhao, and B. G. Shen

Appl. Phys. Lett. 91, 262506 (2007); http://dx.doi.org/10.1063/1.2825473 (3 pages) | Cited 2 times

Online Publication Date: 26 December 2007

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A systematic study on the resistivity-magnetization relation above the Curie temperature (TC) has been performed for the manganites with different properties, such as the epitaxial La0.67Ca0.33MnO3 film on a SrTiO3 substrate, which has the weakest magnetic correlation above TC, the La0.27Nd0.4Ca0.33MnO3 polycrystalline, which exhibits a charge ordering in the paramagnetic state, and the ceramics Eu0.55Sr0.45MnO3 and La0.474Bi0.193Ca0.33Mn0.994Cr0.006O3, which show strong short-range magnetic orders above TC. A quantitative, yet universal, relation of the form ρ = AT exp[(ε-αm2)/T] is observed in all of the manganites, with an essentially constant coefficient of α ≈ 800±60 K, where m is the normalized magnetization and ε is the activation energy for polarons. The underlying physics for this relation has been analyzed based on the double exchange model.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.61.Ng Insulators
75.20.Ck Nonmetals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Ak Magnetic properties of monolayers and thin films

A nuclear magnetic resonance spectrometer for operation around 1 MHz with a sub-10-mK noise temperature, based on a two-stage dc superconducting quantum interference device sensor

L. V. Levitin, R. G. Bennett, A. Casey, B. P. Cowan, C. P. Lusher, J. Saunders, D. Drung, and Th. Schurig

Appl. Phys. Lett. 91, 262507 (2007); http://dx.doi.org/10.1063/1.2828113 (3 pages) | Cited 3 times

Online Publication Date: 26 December 2007

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We have developed a nuclear magnetic resonance spectrometer with a series tuned input circuit for measurements on samples at millikelvin temperatures based on an integrated two-stage superconducting quantum interference device current sensor, with an energy sensitivity ε = 26±1h when operated at 1.4 K. To maximize the sensitivity, both the nuclear magnetic resonance spectrometer pickup coil and tuning capacitor need to be cooled, and the tank circuit parameters should be chosen to equalize the contributions from circulating current noise and voltage noise in the superconducting quantum interference device. A noise temperature TN = 7±2 mK was measured, at a frequency of 0.884 MHz, with the circuit parameters close to optimum.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.71.Ba Superconducting magnets; magnetic levitation devices
84.32.Tt Capacitors

Improving the IcRn product and the reproducibility of high Tc Josephson junctions made by ion irradiation

M. Sirena, X. Fabrèges, N. Bergeal, J. Lesueur, G. Faini, R. Bernard, and J. Briatico

Appl. Phys. Lett. 91, 262508 (2007); http://dx.doi.org/10.1063/1.2828133 (3 pages) | Cited 1 time

Online Publication Date: 26 December 2007

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A simple model has been proposed to explain the spread in the characteristics of high Tc Josephson junctions made by ion irradiation, assuming that the source of dispersion is the slit’s size variation. Accordingly, increasing ion energy should lead to a significant reduction of inhomogeneities. Test samples have been fabricated using two different beam energies. As predicted, the spread in critical current decreases upon increasing energy. Moreover, since the actual width of the barrier is reduced in this case, the IcRn product increases significantly. These results seem promising for future technological applications.
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74.81.Fa Josephson junction arrays and wire networks
85.25.-j Superconducting devices
74.72.-h Cuprate superconductors
61.80.Jh Ion radiation effects
74.25.Sv Critical currents

A cascade switching superconducting single photon detector

M. Ejrnaes, R. Cristiano, O. Quaranta, S. Pagano, A. Gaggero, F. Mattioli, R. Leoni, B. Voronov, and G. Gol’tsman

Appl. Phys. Lett. 91, 262509 (2007); http://dx.doi.org/10.1063/1.2828138 (3 pages) | Cited 40 times

Online Publication Date: 26 December 2007

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We have realized superconducting single photon detectors with reduced inductance and increased signal pulse amplitude. The detectors are based on a parallel connection of ultrathin NbN nanowires with a common bias inductance. When properly biased, an absorbed photon induces a cascade switch of all the parallel wires generating a signal pulse amplitude of 2 mV. The parallel wire configuration lowers the detector inductance and reduces the response time well below 1 ns.
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85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
81.07.-b Nanoscale materials and structures: fabrication and characterization
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Magnetization dynamics in planar spin transfer devices and stabilization by repulsion in a spin-flip transistor

Ya. B. Bazaliy

Appl. Phys. Lett. 91, 262510 (2007); http://dx.doi.org/10.1063/1.2822407 (3 pages) | Cited 2 times

Online Publication Date: 27 December 2007

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In systems with dominating easy-plane anisotropy, magnetization dynamics is governed by effective one dimensional equation for the in-plane angle. Rederiving this equation in the presence of spin torques, we obtain a convenient and intuitive description of spin transfer devices. In the case of a spin-flip transistor, the method provides a surprising prediction: the device can be stabilized in the (normally unstable) energy saddle point by a spin torque repelling from that point. Stabilization by repulsion happens due to the presence of dissipative environment and requires a Gilbert damping constant that is large enough to ensure overdamped dynamics at zero current.
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75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.25.-b Spin polarized transport
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Peculiarities of the extraordinary Hall effect of planar arrays Fe nanoparticles embedded in an ultrathin Pt film

V. T. Volkov, V. I. Levashov, V. N. Matveev, and V. A. Berezin

Appl. Phys. Lett. 91, 262511 (2007); http://dx.doi.org/10.1063/1.2827174 (3 pages) | Cited 2 times

Online Publication Date: 27 December 2007

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The extraordinary Hall effect was investigated for planar arrays Fe nanoparticles embedded in an ultrathin Pt matrix. It was found that the slope of Hall resistance (RH) reversed sign at ±0.15 T for Fe particles of mean thickness 0.3 nm. The dependence is presumably due to the effect of two spin-orbital induced mechanisms of carriers scattering, skew scattering, and side jump, with the skew component of positive sign and the side jump component of negative sign. For Fe samples, 0.6 nm thick RH increases monotonically with the magnetic field value. At low temperatures, the superparamagnetism of the samples disappeared.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Tt Fine-particle systems; nanocrystalline materials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Tuning the perpendicular magnetic anisotropy in tetragonally distorted FexCo1−x alloy films on Rh (001) by varying the alloy composition

F. Luo, X. L. Fu, A. Winkelmann, and M. Przybylski

Appl. Phys. Lett. 91, 262512 (2007); http://dx.doi.org/10.1063/1.2821370 (3 pages) | Cited 8 times

Online Publication Date: 27 December 2007

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Tetragonally distorted FexCo1−x alloy films are grown on Rh (001) showing a strong perpendicular magnetic anisotropy in a wide thickness and composition range. This large perpendicular magnetic anisotropy is chemical composition dependent and reaches a maximum at x = 0.4. For this composition, we observed an out-of-plane easy axis of magnetization at room temperature with film thickness up to 15 ML. Our experiments show that the proper adjustment of the Fermi level (EF) by the variation of the FexCo1−x alloy composition and the corresponding tetragonal distortion results in a large perpendicular magnetic anisotropy.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
71.20.Gj Other metals and alloys

Electron holography study of the temperature variation of the magnetic order parameter within circularly chained nickel nanoparticle rings

Akira Sugawara, Kei-ichi Fukunaga, M. R. Scheinfein, H. Kobayashi, H. Kitagawa, and A. Tonomura

Appl. Phys. Lett. 91, 262513 (2007); http://dx.doi.org/10.1063/1.2827586 (3 pages) | Cited 4 times

Online Publication Date: 27 December 2007

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The magnetic structure within circular chains composed of 30-nm-diameter, polymer-coated nickel particles was studied by electron holography. The magnetic flux closure due to dipolar coupling was confirmed at zero external magnetic field. Its long-range order parameter was determined from the magnitude of the electron phase shift, and it was found to decrease more rapidly than that of bulk nickel as a function of temperature. The results of Monte Carlo simulations indicated that the temperature variation of the order-parameter was explained in terms of weakened dipolar coupling field ascribed to the decay of the bulk magnetization and enhanced thermal fluctuations.
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75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.40.Mg Numerical simulation studies
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.05.Bx Metals, semimetals, and alloys

Electronic structure of Fe-doped In2O3 magnetic semiconductor with oxygen vacancies: Evidence for F-center mediated exchange interaction

Shu-jun Hu, Shi-shen Yan, Xue-ling Lin, Xin-xin Yao, Yan-xue Chen, Guo-lei Liu, and Liang-mo Mei

Appl. Phys. Lett. 91, 262514 (2007); http://dx.doi.org/10.1063/1.2828041 (3 pages) | Cited 20 times

Online Publication Date: 27 December 2007

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Based on the first-principles calculations, the electronic structure and magnetic properties of Fe-doped In2O3 were theoretically investigated. The presence of the predominating defects in oxide, i.e., oxygen vacancies, can lead to strong ferromagnetic coupling between the nearest neighboring Fe cations. Spin density and band-projected charge distribution in the vicinity of the oxygen vacancies reveal that the ferromagnetic exchange is mediated by the donor impurity state, which mainly consists of Fe:3d and Fe:4s electrons trapped in oxygen vacancies. Such results provide direct evidence for the F-center mediated exchange interaction in oxide-based magnetic semiconductors.
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75.50.Pp Magnetic semiconductors
71.20.Ps Other inorganic compounds
75.30.Et Exchange and superexchange interactions
71.15.-m Methods of electronic structure calculations
75.50.Dd Nonmetallic ferromagnetic materials

Electronic transport and magnetoresistance in ultrathin manganite-titanate junctions

Y. W. Xie, J. R. Sun, Y. N. Han, and B. G. Shen

Appl. Phys. Lett. 91, 262515 (2007); http://dx.doi.org/10.1063/1.2828135 (3 pages) | Cited 3 times

Online Publication Date: 28 December 2007

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We present a systematic study on the rectifying behaviors of the heterojunctions composed of a ultrathin La0.67Sr0.33MnO3 film ( ∼ 2 nm in thickness) and a SrTiO3 substrate doped by 0.05 or 1 wt % Nb. These junctions exhibit excellent rectifying behaviors and a remarkable bias-dependent magnetoresistance (up to 60% under a field of 5 T). The transport behaviors are dominated by thermal process and tunneling process for the junctions with low and high Nb contents, respectively.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
72.20.My Galvanomagnetic and other magnetotransport effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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