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23 May 2005

Volume 86, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 86, 213111 (2005); http://dx.doi.org/10.1063/1.1931027 (3 pages)

R. H. Miwa, W. Orellana, and A. Fazzio
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Spin-polarized electron tunneling across magnetic dielectric

I. V. Shvets, A. N. Grigorenko, K. S. Novoselov, and D. J. Mapps

Appl. Phys. Lett. 86, 212501 (2005); http://dx.doi.org/10.1063/1.1925785 (3 pages) | Cited 1 time

Online Publication Date: 16 May 2005

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This letter deals with a magnetic tunnel junction having spin filtering by a magnetic barrier. We performed experiments in which a relatively strong external field rotates magnetizations of both ferromagnetic electrodes in the tunnel junction with the magnetic barrier simultaneously so that the two are always parallel to each other. The tunnel magnetoresistance induced in this way was over 16% at 300 K. The angular dependency of the tunnel current on the layer magnetizations indicates that the barrier contains antiferromagnetic oxide. To achieve the described effect the magnetic electrode of the junction was oxidized prior to forming the Al2O3 layer.
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75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys
72.25.Ba Spin polarized transport in metals
75.47.Np Metals and alloys
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Universal relationship between crystallinity and irreversibility field of MgB2

A. Yamamoto, J. Shimoyama, S. Ueda, Y. Katsura, I. Iwayama, S. Horii, and K. Kishio

Appl. Phys. Lett. 86, 212502 (2005); http://dx.doi.org/10.1063/1.1937991 (3 pages) | Cited 67 times

Online Publication Date: 18 May 2005

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The relationship between irreversibility field, Hirr, and crystallinity of MgB2 bulks including carbon substituted samples was studied. The Hirr was found to increase with an increase of full width at half maximum (FWHM) of MgB2 (110) peak, which corresponds to distortion of honeycomb boron sheet, and their universal correlation was discovered even including carbon substituted samples. Excellent Jc characteristics under high magnetic fields were observed in samples with large FWHM of (110) due to the enhanced intraband scattering and strengthened grain boundary flux pinning. The relationship between crystallinity and Hirr can explain the large variation of Hirr for MgB2 bulks, tapes, single crystals, and thin films.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Op Mixed states, critical fields, and surface sheaths
74.25.Ha Magnetic properties including vortex structures and related phenomena
61.66.Fn Inorganic compounds
61.72.Mm Grain and twin boundaries

Superconducting vortex profile from fixed point measurements the “Lazy Fisherman” tunneling microscopy method

A. Kohen, T. Cren, Th. Proslier, Y. Noat, W. Sacks, D. Roditchev, F. Giubileo, F. Bobba, A. M. Cucolo, N. Zhigadlo, S. M. Kazakov, and J. Karpinski

Appl. Phys. Lett. 86, 212503 (2005); http://dx.doi.org/10.1063/1.1939077 (3 pages) | Cited 8 times

Online Publication Date: 18 May 2005

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We introduce a mode of operation for studying the vortex phase in superconductors using scanning tunneling microscopy (STM). While in the conventional STM method, the tip is scanned over a sample in which a fixed vortex pattern is prepared, in our “Lazy Fisherman” method the STM tip is kept fixed at a selected location while the vortices are being moved by varying the applied magnetic field. By continuously acquiring the local tunneling conductance spectra, dI/dV(V), we detect the changes in the local density of states under the tip due to the vortex motion. With no need for scanning, the method permits one to extend the study of vortices to samples in which scanning is difficult or even impossible due to surface nonuniformity and allows one to study vortex dynamics. Using a statistical analysis of the spectra, we reconstruct the single vortex zero bias conductance profile. We apply the method to the c-axis face of a MgB2 single crystal sample and obtain a vortex profile with a coherence length, ξ of 57±2 nm.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.F- Transport properties
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Jb Electronic structure (photoemission, etc.)
74.50.+r Tunneling phenomena; Josephson effects

Influence of nitrogen growth pressure on the ferromagnetic properties of Cr-doped AlN thin films

Jun Zhang, X. Z. Li, B. Xu, and D. J. Sellmyer

Appl. Phys. Lett. 86, 212504 (2005); http://dx.doi.org/10.1063/1.1940131 (3 pages) | Cited 20 times

Online Publication Date: 19 May 2005

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We report the magnetic properties of Cr-doped AlN thin films grown by reactive magnetron sputtering under various nitrogen pressures. Ferromagnetism is observed up to the highest temperature measured, 400 K, and shows strong dependence on the Cr concentration and, especially, the nitrogen growth pressure. By varying the nitrogen pressure during film growth, the magnetic properties of the films can be changed while keeping a constant Cr concentration. The ferromagnetism is enhanced in the films that were grown at low nitrogen pressures and thus nitrogen deficient, suggesting an important role of defects in the ferromagnetism of this material.
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75.50.Pp Magnetic semiconductors
81.05.Ea III-V semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering

Strong near-infrared photoluminescence in erbium/ytterbium codoped porous silicon

L. Luo, X. X. Zhang, K. F. Li, K. W. Cheah, M. L. Gong, J. X. Shi, and W. K. Wong

Appl. Phys. Lett. 86, 212505 (2005); http://dx.doi.org/10.1063/1.1925776 (3 pages) | Cited 4 times

Online Publication Date: 19 May 2005

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Erbium ions and ytterbium ions (1021/cm3) were electrochemically codoped into porous silicon. When compared with the Er-doped porous silicon we found two salient features in its photoluminescence. One is that the 1.54 μm emission of Er3+ ions was 50 times stronger under 980 nm laser excitation at room temperature. This is due to the high efficiency of the Yb3+→Er3+ energy transfer. The other is that the photoluminescence intensity increases rapidly with temperature, while that in Er-doped porous silicon decreases monotonically with temperature. Our results show that the codoped Er/Yb porous silicon has a promising potential for the application in optical communications.
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81.05.Cy Elemental semiconductors
78.55.Ap Elemental semiconductors
61.72.uf Ge and Si
78.30.Am Elemental semiconductors and insulators
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