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14 Jul 2003

Volume 83, Issue 2, pp. 207-403

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Appl. Phys. Lett. 83, 225 (2003); http://dx.doi.org/10.1063/1.1591241 (3 pages)

A. Borowiec, D. M. Bruce, Daniel T. Cassidy, and H. K. Haugen
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Intense vortex pinning enhanced by semicrystalline defect traps in self-aligned nanostructured MgB2

S. Li, T. White, K. Laursen, T. T. Tan, C. Q. Sun, Z. L. Dong, Y. Li, S. H. Zho, J. Horvat, and S. X. Dou

Appl. Phys. Lett. 83, 314 (2003); http://dx.doi.org/10.1063/1.1591070 (3 pages) | Cited 12 times

Online Publication Date: 8 July 2003

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In this work, we report the discovery of a vortex pinning source: semicrystalline defect wells in self-aligned nanostructured MgB2. It is demonstrated that these aperiodic regions trap numerous crystal defects migrating along nanodomain boundaries during self-alignment and act as intense vortex pinning centers that significantly enhance the high-field performance of MgB2. This suggests that the density of trapped defects in the wells is much greater than that found in other vortex pinning sources. © 2003 American Institute of Physics.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
61.46.-w Structure of nanoscale materials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Yx Interaction between different crystal defects; gettering effect

Effect of Zr concentration on the microstructure of Al and the magnetoresistance properties of the magnetic tunnel junction with a Zr-alloyed Al–oxide barrier

Seong-Rae Lee, Chul-Min Choi, and Young Keun Kim

Appl. Phys. Lett. 83, 317 (2003); http://dx.doi.org/10.1063/1.1592312 (3 pages) | Cited 21 times

Online Publication Date: 8 July 2003

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We studied the composition dependence of the microstructure of Al–Zr alloy films and the tunneling magnetoresistance (TMR) behavior of magnetic tunnel junctions (MTJ) with a Zr-alloyed Al–oxide barrier. A highly stable MTJ with a superior-quality 9.89 at. % Zr alloyed Al–oxide barrier was achieved with 39.5% TMR and a bias voltage of 711 mV at half (Vh) TMR. The microstructure of Al changed systematically from polycrystalline to single phase amorphous to duplex phases composed of an amorphous Al–Zr phase and a crystalline AlZr compound, probably Al3Zr, as the Zr concentration increased. The microstructure of the Al–Zr alloy before oxidation has a dominant effect on the TMR characteristics and MTJ stability. A single amorphous Al–Zr alloy ( ∼ 10 at. % Zr) film has superior surface uniformity; consequently, an ultrahigh-quality oxide barrier was formed after oxidation. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
68.35.Ct Interface structure and roughness
72.25.Mk Spin transport through interfaces
81.65.Mq Oxidation

Dc-transport properties of ferromagnetic (Ga,Mn)As semiconductors

T. Jungwirth, Jairo Sinova, K. Y. Wang, K. W. Edmonds, R. P. Campion, B. L. Gallagher, C. T. Foxon, Qian Niu, and A. H. MacDonald

Appl. Phys. Lett. 83, 320 (2003); http://dx.doi.org/10.1063/1.1590433 (3 pages) | Cited 12 times

Online Publication Date: 8 July 2003

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We study the dc transport properties of (Ga,Mn)As diluted magnetic semiconductors with Mn concentration varying from 1.5% to 8%. Both diagonal and Hall components of the conductivity tensor are strongly sensitive to the magnetic state of these semiconductors. Transport data obtained at low temperatures are discussed theoretically within a model of band-hole quasiparticles with a finite spectral width due to elastic scattering from Mn and compensating defects. The theoretical results are in good agreement with measured anomalous Hall effect and anisotropic longitudinal magnetoresistance data. © 2003 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.47.Pq Other materials
75.50.Dd Nonmetallic ferromagnetic materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects
75.70.Ak Magnetic properties of monolayers and thin films

Materials dependence of the spin-momentum transfer efficiency and critical current in ferromagnetic metal/Cu multilayers

M. R. Pufall, W. H. Rippard, and T. J. Silva

Appl. Phys. Lett. 83, 323 (2003); http://dx.doi.org/10.1063/1.1590432 (3 pages) | Cited 34 times

Online Publication Date: 8 July 2003

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We have quantitatively compared spin-momentum transfer effects in FM/Cu multilayers, with FM = Co, Co90Fe10, Ni80Fe20, Ni40Fe10Cu50, and Fe. All of the measured multilayers exhibited an abrupt step up in resistance at a critical current Ic, the value of which was a linear function of applied magnetic field Happ. The spin-transfer efficiencies determined from these data were in substantial agreement with their predicted values over the range of materials studied. Ic(Happ), when evaluated at zero net field, was found to increase with the exchange energy density of the ferromagnet, demonstrating the tunability of the critical current by materials selection.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.30.Et Exchange and superexchange interactions

High critical current densities in Cu-sheathed MgB2 formed from a mechanically-alloyed precursor

N. M. Strickland, R. G. Buckley, and A. Otto

Appl. Phys. Lett. 83, 326 (2003); http://dx.doi.org/10.1063/1.1584785 (3 pages) | Cited 11 times

Online Publication Date: 8 July 2003

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Mechanical alloying is used to produce a metallic precursor for MgB2 formation. Micron-scale mixing of magnesium and boron powders allows the MgB2 formation reaction to proceed at as low as 450 °C, with high-quality material formed in an hour at 600 °C. These low reaction temperatures allow the reaction to be performed in situ in a copper sheath. Critical current densities, calculated from a full critical-state simulation of magnetization hysteresis loops, are up to 7×105 A/cm2 at 13.6 K and 1×105 A/cm2 at 30 K, in zero applied field. © 2003 American Institute of Physics.
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84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena
82.20.-w Chemical kinetics and dynamics

Magnetization configuration and switching behavior of submicron NiFe elements: Pac-man shape

M. H. Park, Y. K. Hong, S. H. Gee, D. W. Erickson, and B. C. Choi

Appl. Phys. Lett. 83, 329 (2003); http://dx.doi.org/10.1063/1.1592002 (3 pages) | Cited 24 times

Online Publication Date: 8 July 2003

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Two types of submicron permalloy element, namely Pac-man, were investigated by a magnetic force microscope for magnetization configuration and switching behaviors. Two distinct domain configurations, bidomain for Pac-man type I and single domain for Pac-man type II, were observed in arrays of Pac-man elements. The domain configuration depends on the slot angle for the Pac-man type I, but is independent of the slot angle for the Pac-man type II. Array of Pac-man elements with a slot angle of 180° shows the highest switching field and the narrowest switching field distribution, as compared to rectangular and hexagonal elements of the same overall dimensions. © 2003 American Institute of Physics.
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75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.37.Rt Magnetic force microscopy (MFM)
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Relaxation times in exchange-biased nanostructures

José Mejía-López, D. Altbir, and Iván K. Schuller

Appl. Phys. Lett. 83, 332 (2003); http://dx.doi.org/10.1063/1.1592637 (3 pages) | Cited 7 times

Online Publication Date: 8 July 2003

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We calculated the energy barrier, ΔE, for exchange-biased (EB) systems, using the ferromagnetic domain wall model. The temperature dependence of the EB is in good agreement with experimental results. For Fe–FeF2, Fe–MnF2, and Ni–NiO, ΔE is proportional to a power of the interfacial coupling constant and inversely to the ferromagnetic film thickness. The temperature and volume dependence of the relaxation time show that exchange coupling increases the superparamagnetic blocking temperature of nanostructured ferromagnets. © 2003 American Institute of Physics.
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75.75.-c Magnetic properties of nanostructures
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ch Domain walls and domain structure
75.50.Ee Antiferromagnetics
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