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29 Dec 2003

Volume 83, Issue 26, pp. 5347-5569

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Appl. Phys. Lett. 83, 5527 (2003); http://dx.doi.org/10.1063/1.1637143 (3 pages)

Chad R. Barry, Nyein Z. Lwin, Wei Zheng, and Heiko O. Jacobs
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Observation of the barrier structure in magnetic tunnel junctions using high-resolution electron microscopy and electron holography

F. Shen, T. Zhu, X. H. Xiang, John Q. Xiao, E. Voelkl, and Z. Zhang

Appl. Phys. Lett. 83, 5482 (2003); http://dx.doi.org/10.1063/1.1637129 (3 pages) | Cited 8 times

Online Publication Date: 22 December 2003

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Microstructures of the NiFe/AlOx/NiFe magnetic tunnel junctions and the barrier shape profile have been studied with atomic resolution using high-resolution electron microscopy and electron holography. A clear relationship between the growth morphologies of the electrodes and the quality of the barrier has been obtained. Although the bottom interface between electrode and barrier is very sensitive to the oxidation condition, a sharp interface can be achieved in optimumally oxidized junctions. The top interface, on the other hand, is always slightly oxidized due to the three-dimensional growth of top electrode above the barrier, independent of the oxidation condition of the barrier. Furthermore, charge accumulation seems to exist at the sharp interfaces. It is also interesting, yet surprising, that both interfaces are actually sharp in underoxidized junctions. Furthermore, charge accumulation seems to exist at the sharp interfaces. © 2003 American Institute of Physics.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Electronic and magnetic properties of MnAs nanoclusters studied by x-ray absorption spectroscopy and x-ray magnetic circular dichroism

J. Okabayashi, M. Mizuguchi, M. Oshima, H. Shimizu, M. Tanaka, M. Yuri, and C. T. Chen

Appl. Phys. Lett. 83, 5485 (2003); http://dx.doi.org/10.1063/1.1637430 (3 pages) | Cited 2 times

Online Publication Date: 22 December 2003

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We have investigated the electronic and magnetic properties of a MnAs:GaAs granular film with MnAs clusters embedded in the GaAs matrix fabricated by high-temperature annealing of Ga1−xMnxAs using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The XAS line shapes in the Mn 2p core level changed from a localized structure to an itinerant NiAs-type one. Magnetic-field dependence of the XMCD revealed no hysteresis curves at the fixed photon energy where the large XMCD signals were observed, suggesting the superparamagnetic behavior at 100 K. © 2003 American Institute of Physics.
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73.22.-f Electronic structure of nanoscale materials and related systems
75.50.Tt Fine-particle systems; nanocrystalline materials
78.70.Dm X-ray absorption spectra
75.20.Ck Nonmetals
81.07.Bc Nanocrystalline materials
81.40.Gh Other heat and thermomechanical treatments

Ferromagnetism in cobalt-implanted ZnO

D. P. Norton, M. E. Overberg, S. J. Pearton, K. Pruessner, J. D. Budai, L. A. Boatner, M. F. Chisholm, J. S. Lee, Z. G. Khim, Y. D. Park, and R. G. Wilson

Appl. Phys. Lett. 83, 5488 (2003); http://dx.doi.org/10.1063/1.1637719 (3 pages) | Cited 83 times

Online Publication Date: 22 December 2003

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The magnetic and structural properties of cobalt-implanted ZnO single crystals are reported. High-quality, (110)-oriented single-crystal Sn-doped ZnO substrates were implanted at ∼ 350 °C with Co to yield transition metal concentrations of 3–5 at. % in the near-surface (∼2000 Å) region. After implantation, the samples were subject to a 5 min rapid thermal annealing at 700 °C. Magnetization measurements indicate ferromagnetic behavior, with hysteresis observed in the M vs H behavior at T = 5 K. Coercive fields were ⩽100 Oe at this measurement temperature. Temperature-dependent magnetization measurements showed evidence for ordering temperatures of >300 K, although hysteresis in the M vs H behavior was not observed at room temperature. Four-circle x-ray diffraction results indicate the presence of (110)-oriented hexagonal phase Co in the ZnO matrix. From the 2θ full width at half maximum (FWHM) of the Co (110) peak, the nanocrystal size is estimated to be ∼3.5 nm, which is below the superparamagnetic limit at room temperature. In-plane x-ray diffraction results show that the nanocrystals are epitaxial with respect to the ZnO host matrix. The magnetic properties are consistent with the presence of Co nanocrystals, but do not preclude the possibility that a component of the magnetism is due to Co substitution on the Zn site in the ZnO matrix. © 2003 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Pp Magnetic semiconductors
81.05.Dz II-VI semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
75.50.Tt Fine-particle systems; nanocrystalline materials

Electronic structures and the estimated Curie temperatures of (Ga1−yIny)1−xMnxAs

K. Miura, M. Iwasawa, S. Imanaga, and T. Ami

Appl. Phys. Lett. 83, 5491 (2003); http://dx.doi.org/10.1063/1.1638632 (3 pages) | Cited 2 times

Online Publication Date: 22 December 2003

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The electronic structures of (Ga1−yIny)1−xMnxAs have been investigated using the Korringa, Kohn and Rostoker (KKR) method with the coherent potential approximation (CPA). The estimated Curie temperature (TC) of Ga1−xMnxAs is higher than that of (Ga0.5In0.5)1−xMnxAs and In1−xMnxAs when x≲0.10. On the other hand, the estimated TC of Ga1−xMnxAs saturates with an increase of x when x≳0.05, but that of (Ga0.5In0.5)1−xMnxAs and In1−xMnxAs does not saturate even when x>0.10. These results are in good agreement with the previous experimental results. Our calculated results predict that the TC of (Ga0.5In0.5)1−xMnxAs and In1−xMnxAs will be higher than that of Ga1−xMnxAs when x≳0.10. © 2003 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.20.Nr Semiconductor compounds
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Lk Spin glasses and other random magnets
75.10.Lp Band and itinerant models
71.15.-m Methods of electronic structure calculations
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