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18 Jul 2005

Volume 87, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 87, 033501 (2005); http://dx.doi.org/10.1063/1.1992665 (3 pages)

Yoshihito Miyoshi, Fumito Nakajima, Junichi Motohisa, and Takashi Fukui
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Crossover from negative to positive magnetoresistance in La0.7Ce0.3MnO3-SrTiO3-Nb heterojunctions

Z. G. Sheng, W. H. Song, Y. P. Sun, J. R. Sun, and B. G. Shen

Appl. Phys. Lett. 87, 032501 (2005); http://dx.doi.org/10.1063/1.1995960 (3 pages) | Cited 20 times

Online Publication Date: 11 July 2005

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A crossover from negative to positive magnetoresistance (MR) is observed in the heterojunction composed of a La0.7Ce0.3MnO3 film and a 0.5 wt. % Nb-doped SrTiO3 substrate. The temperature and bias current dependences of MR sign in the junction are investigated carefully. It is found that the positive MR occurs when temperature or applied bias current is increased to a higher value. The relation between MR and an external magnetic field is also found to be temperature dependent. We attribute the appearance of the positive MR at higher temperatures to the tunneling transport mechanism. These results are helpful in configuring artificial devices using manganite-based heterojunctions.
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75.47.Lx Magnetic oxides
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Electron spin injection into GaAs from ferromagnetic contacts in remanence

N. C. Gerhardt, S. Hövel, C. Brenner, M. R. Hofmann, F.-Y. Lo, D. Reuter, A. D. Wieck, E. Schuster, W. Keune, and K. Westerholt

Appl. Phys. Lett. 87, 032502 (2005); http://dx.doi.org/10.1063/1.1996843 (3 pages) | Cited 25 times

Online Publication Date: 12 July 2005

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We demonstrate electrical spin injection into a (GaIn)As/GaAs light-emitting diode from the remanent state of ferromagnetic contacts in perpendicular geometry. Using a Fe/Tb multilayer structure with perpendicular magnetic anisotropy and a reverse-biased Schottky contact, we achieve a circular polarization degree of the emitted light of 0.75% at 90 K.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts

Magnetically superior and easy to handle L10-FePt nanocrystals

Shinpei Yamamoto, Yasumasa Morimoto, Teruo Ono, and Mikio Takano

Appl. Phys. Lett. 87, 032503 (2005); http://dx.doi.org/10.1063/1.1995959 (3 pages) | Cited 45 times

Online Publication Date: 12 July 2005

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We report synthesis of monodisperse L10-FePt nanocrystals that are not only superior in magnetism but also easy to handle through being dispersible in solvents. Thanks to a thick SiO2 coating, the thermal treatment needed to form the L10 structure can be done even at 900 °C without inducing coalescence and coarsening. The protecting shell was thereafter removed in a specific way that enabled us to recover the L10-FePt nanocrystals in a water dispersion. The SiO2-coated nanocrystals show a high coercivity of 18.5 kOe at room temperature in spite of their core size of only 6.5 nm in diameter, and the hysteresis loop of the water-dispersed nanocrystals, which were frozen under an external field, was almost rectangular indicating that their magnetic and structural orientation could be attained.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ss Magnetic recording materials
81.07.Bc Nanocrystalline materials
81.40.Gh Other heat and thermomechanical treatments
61.46.-w Structure of nanoscale materials

Low-temperature ordering of FePt thin films by a thin AuCu underlayer

Yun Zhu and J. W. Cai

Appl. Phys. Lett. 87, 032504 (2005); http://dx.doi.org/10.1063/1.1997268 (3 pages) | Cited 28 times

Online Publication Date: 14 July 2005

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We have studied the magnetic and structural properties of AuCu(0–50 nm)/FePt(2–50 nm) films after annealing at various temperatures. The results indicate that, by introducing a thin equiatomic AuCu underlayer, the ordering temperature of FePt films with thickness even down to 5 nm can be significantly reduced to 350 °C, at which a large coercivity is developed. In fact, the coercivity is as high as 4.6 kOe for a 5 nm FePt film on a 10 nm AuCu underlayer after annealing at 350 °C and this value is raised up to 7.5 kOe when annealed at 400 °C, while the corresponding sample without a AuCu underlayer has to be annealed at a temperature beyond 600 °C in order to achieve a coercivity of 4 kOe. The ordering of the thin AuCu film at relatively low temperature and thus coherently inducing the ordering of FePt film led to the formation of the ordered FePt phase at a much lowered temperature.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ss Magnetic recording materials
75.50.Vv High coercivity materials
81.40.Gh Other heat and thermomechanical treatments
68.55.-a Thin film structure and morphology
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