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3 Nov 2003

Volume 83, Issue 18, pp. 3647-3835

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 3737 (2003); http://dx.doi.org/10.1063/1.1623315 (3 pages)

Ian Appelbaum, D. J. Monsma, K. J. Russell, V. Narayanamurti, and C. M. Marcus
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Spin-valve photodiode

Ian Appelbaum, D. J. Monsma, K. J. Russell, V. Narayanamurti, and C. M. Marcus

Appl. Phys. Lett. 83, 3737 (2003); http://dx.doi.org/10.1063/1.1623315 (3 pages) | Cited 8 times

Online Publication Date: 28 October 2003

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An optical spin-valve effect is observed using sub-bandgap internal photoemission to generate and collect hot electrons in magnetic multilayers grown on n-Si. Approximately 1.5%–2.5% magnetoresistance is observed in this two-terminal device at low temperature, and this effect is reduced only to 1.1% at room temperature. A simple model is presented to explain the results. © 2003 American Institute of Physics.
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72.25.Fe Optical creation of spin polarized carriers
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.21.Ac Multilayers
85.60.Dw Photodiodes; phototransistors; photoresistors
73.50.Fq High-field and nonlinear effects
73.50.Mx High-frequency effects; plasma effects

Correlation between the superconducting and structural properties in MgB2 thin films prepared by molecular-beam epitaxy

Hiroki Yamazaki, Yasuyuki Hikita, Hiroki Hori, and Hidenori Takagi

Appl. Phys. Lett. 83, 3740 (2003); http://dx.doi.org/10.1063/1.1623323 (3 pages) | Cited 3 times

Online Publication Date: 28 October 2003

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Superconducting MgB2 films were prepared on an Al2O3(0001) substrate by codeposition of Mg and B using the molecular-beam epitaxy technique and the effects of the growth conditions on the structural and the superconducting properties were extensively investigated. The superconducting transition temperature Tc shows a peak as a function of the deposition-rate ratio of Mg to B2 and the stoichiometric composition is likely realized at the Tc peak. The optimum substrate temperature Ts was found to be 330 °C. Detailed structural characterizations indicate the strong suppression of structural coherence in the stoichiometric and Mg-rich films. This accounts for the fact that optimized Tc (26.6 K) is still lower than bulk Tc like in previous molecular-beam epitaxy studies. We argue that such structural disorder originates from epitaxial strain due to the lattice mismatch between the film and the substrate. © 2003 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
74.78.-w Superconducting films and low-dimensional structures
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
68.55.-a Thin film structure and morphology
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Magnetoresistance in boron carbide junctions

L. Bernard, J. Monson, A. Sokolov, Zong-Yuan Liu, C.-S. Yang, P. A. Dowben, B. Doudin, A. Harken, P. Welsch, and B. W. Robertson

Appl. Phys. Lett. 83, 3743 (2003); http://dx.doi.org/10.1063/1.1621072 (3 pages) | Cited 8 times

Online Publication Date: 28 October 2003

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Photoemission and electric transport properties of ferromagnet–insulator–ferromagnet junctions with boron carbide (C2B10) dielectric barrier are presented. Using a non-oxide barrier confidence avoids oxidation of the interfaces with the ferromagnetic layers. Photoemission confirms chemical abruptness of the interface. Magnetoresistance ratios reaching 50% are observed at low temperatures, and large nonlinearity in the current–voltage curves show that impurities in the junctions play a key role. © 2003 American Institute of Physics.
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73.40.Rw Metal-insulator-metal structures
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
79.60.Jv Interfaces; heterostructures; nanostructures

Ferromagnetism in Mn-doped CuO

S. G. Yang, T. Li, B. X. Gu, Y. W. Du, H. Y. Sung, S. T. Hung, C. Y. Wong, and A. B. Pakhomov

Appl. Phys. Lett. 83, 3746 (2003); http://dx.doi.org/10.1063/1.1623944 (3 pages) | Cited 33 times

Online Publication Date: 28 October 2003

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Ferromagnetic properties have been observed in CuO doped with 3.5–15 at. % of Mn. The transition from ferromagnetic to paramagnetic phase at TC = 80 K is associated with the metal–insulator transition. Magnetoresistance is weakly negative in the vicinity of the transition, but positive in a wide range of temperatures below TC. The experimental results suggest a possibility of interpretation in terms of the Zener double-exchange mechanism and strong electron–phonon interactions. © 2003 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.47.Pq Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.60.+g Mixed conductivity and conductivity transitions
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.Hg Electrical injection of spin polarized carriers
75.30.Et Exchange and superexchange interactions
63.20.K- Phonon interactions
72.80.Ga Transition-metal compounds

Recording potential of a single-domain particle

N. A. Usov, Ching-Ray Chang, and Zung-Hang Wei

Appl. Phys. Lett. 83, 3749 (2003); http://dx.doi.org/10.1063/1.1623921 (3 pages) | Cited 4 times

Online Publication Date: 28 October 2003

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The ratio of the coercive force Hc to the effective energy barrier Uef is introduced to characterize the recording capability of a single-domain particle. It is shown that this ratio depends on the shape of the energy barrier separating equivalent energy minima. The optimal shape of the barrier is obtained for particles with uniaxial and combined (both uniaxial and cubic) types of magnetic anisotropy. For the optimal shapes, the gain in the ratio Hc/Uef can achieve 20%–40% with respect to the case of a Stoner–Wohlfarth particle. © 2003 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure

Behavior of magnetic domains during structural transformations in Ni2MnGa ferromagnetic shape memory alloy

H. S. Park, Y. Murakami, D. Shindo, V. A. Chernenko, and T. Kanomata

Appl. Phys. Lett. 83, 3752 (2003); http://dx.doi.org/10.1063/1.1624633 (3 pages) | Cited 22 times

Online Publication Date: 28 October 2003

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Change in the magnetic domain structure of Ni2MnGa Heusler alloy with the structural transformation from the parent phase to the intermediate phase and subsequent transformation to the martensite was studied by in situ observations using Lorentz microscopy and electron holography. Both the parent phase and the intermediate phase showed peculiar stripe magnetic domains, and the observed magnetization distribution was similar to each other. In contrast, the magnetization distribution was dramatically modified by the transformation to the tetragonal martensite. The observation appears to indicate that the magnetization distribution in the parent phase can interact with the short-wave lattice distortions to generate the intermediate phase, via the magnetoelastic interaction, resulting in the inheritance of the original magnetization distribution into the intermediate phase. © 2003 American Institute of Physics.
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75.60.Ch Domain walls and domain structure
75.50.Cc Other ferromagnetic metals and alloys
62.20.F- Deformation and plasticity
64.70.K- Solid-solid transitions
81.30.Kf Martensitic transformations
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction
81.40.Lm Deformation, plasticity, and creep

Nonrandom percolation behavior of grain boundary networks in high-Tc superconductors

M. Frary and C. A. Schuh

Appl. Phys. Lett. 83, 3755 (2003); http://dx.doi.org/10.1063/1.1624490 (3 pages) | Cited 15 times

Online Publication Date: 28 October 2003

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The grain boundary networks of tetragonal and orthorhombic superconductors are shown to be nonrandom through computer simulations of polycrystalline structures. For biaxially textured microstructures, the distribution of low-angle grain boundaries around triple junctions is measurably deviant from the expectations for a randomly constructed lattice. Percolation thresholds are calculated for the unhindered flow of superconducting current through a polycrystal, and are found to be significantly different from the standard random percolation threshold in two dimensions. These deviations are explained as a result of crystallographic constraints on the network topology. © 2003 American Institute of Physics.
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74.25.F- Transport properties
74.72.-h Cuprate superconductors
61.72.Mm Grain and twin boundaries

Field-effect experiments in NdBa2Cu3O7−δ ultrathin films using a SrTiO3 single-crystal gate insulator

D. Matthey, S. Gariglio, and J.-M. Triscone

Appl. Phys. Lett. 83, 3758 (2003); http://dx.doi.org/10.1063/1.1624635 (3 pages) | Cited 27 times

Online Publication Date: 28 October 2003

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We report on the electrostatic modulation of superconductivity in very thin films of cuprate superconductors using a field-effect device based on a SrTiO3 single-crystal gate insulator. A Tc modulation of 3.5 K and a 37% change of the normal state resistance have been observed in an epitaxial bilayer composed of an insulating PrBa2Cu3O7−δ layer deposited on top of a superconducting NdBa2Cu3O7−δ film, two unit cells thick. To achieve large electric fields, the thickness of the commercial dielectric single-crystal SrTiO3 substrate (also used as the gate insulator) was reduced to 110 μm. The dielectric properties of the gate insulator were characterized as a function of temperature and electric field and the magnitude of the field effect was quantified. A Tc enhancement of 2.8 K was obtained for an applied field of −1.8×106 V/m, corresponding to a polarization of −4 μC/cm2. © 2003 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.62.Yb Other effects

Magnetization reversal under nonuniform magnetic fields at conditions relevant to magnetic random access memory applications

K. S. Kim, C. E. Lee, and S. H. Lim

Appl. Phys. Lett. 83, 3761 (2003); http://dx.doi.org/10.1063/1.1625105 (3 pages) | Cited 1 time

Online Publication Date: 28 October 2003

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Magnetization reversal behavior is examined under various nonuniform fields, the conditions of which are relevant to magnetic random access memory applications. During the magnetization reversal, the end domains play a key role at a uniform field, but they play a negligible role at a nonuniform field. Instead, a ripple pattern is initially formed in the interior and it progresses to form a vortex, resulting in a reversed domain. The switching field is found to be greater in the case of a nonuniform field, but, under a bias field, it is reduced greatly to a level similar to that for a uniform field. This result may indicate a wide window for the bit selectivity under a nonuniform field in magnetic random access memory applications. © 2003 American Institute of Physics.
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75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Atomic-scale depth selectivity of soft x-ray resonant Kerr effect

Ki-Suk Lee, Sang-Koog Kim, and J. B. Kortright

Appl. Phys. Lett. 83, 3764 (2003); http://dx.doi.org/10.1063/1.1622123 (3 pages) | Cited 13 times

Online Publication Date: 28 October 2003

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By the use of resonant soft x-ray Kerr rotation measurements with its varying incident angle and energy, we observed various shifts of the exchange bias field of a 3.5-nm-thick Co layer in oppositely exchange-biased Ni81Fe19/Fe50Mn50/Co/Pd films. The results in conjunction with their model simulations clearly reveal that the measurements enable one to resolve varying magnetization with depth in the individual magnetic layers of such a multicomponent ultrathin layered structure on the atomic scales. Significant interference effects combined with penetration depth of resonant soft x rays, which are closely associated with their absorptive and refractive contributions, offer remarkably different depth sensitivities into the Kerr effects depending on grazing angle and resonance energy. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
75.50.Cc Other ferromagnetic metals and alloys
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
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