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17 Nov 2003

Volume 83, Issue 20, pp. 4083-4258

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 4238 (2003); http://dx.doi.org/10.1063/1.1627935 (3 pages)

H. B. Peng, T. G. Ristroph, G. M. Schurmann, G. M. King, J. Yoon, V. Narayanamurti, and J. A. Golovchenko
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Direct observation of magnetic bit transition and physical grain boundary in perpendicular recording media

Jun Yu, Joachim Ahner, and Dieter Weller

Appl. Phys. Lett. 83, 4208 (2003); http://dx.doi.org/10.1063/1.1627940 (3 pages) | Cited 1 time

Online Publication Date: 12 November 2003

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The correlation between magnetic bit transition line and physical grain boundary in a multilayer perpendicular recording medium is examined by combined magnetic force and electrostatic force microscopy. Reducing the scan height results in stronger electrostatic interaction between the tip and the sample disk. This electrostatic interaction causes the topographical information to be superimposed onto the magnetic force image and allows simultaneous imaging of the columnar grains and the magnetic bits. It is found that the magnetic transition follows the physical grain boundaries with high accuracy. The correlation of both is quantified by image processing and a correlation coefficient of 0.92 has been determined. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ss Magnetic recording materials
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Mm Grain and twin boundaries

Modification of ferromagnetism in semiconductors by molecular monolayers

T. C. Kreutz, E. G. Gwinn, R. Artzi, R. Naaman, H. Pizem, and C. N. Sukenik

Appl. Phys. Lett. 83, 4211 (2003); http://dx.doi.org/10.1063/1.1625422 (3 pages) | Cited 12 times

Online Publication Date: 12 November 2003

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We report that adsorption of monolayers of organic molecules onto the surface of ferromagnetic semiconductor heterostructures produces large, robust changes in their magnetic properties. The heterostructures have half a monolayer of MnAs embedded in GaAs, 50 Å beneath the surface. The molecules investigated are alkylphosphonic acids that bind to GaAs via a phosphonate group. The organization of the organic monolayer determines the reduction in the Curie temperature, with ordered monolayers producing nearly complete suppression of ferromagnetism. We attribute this striking chemical modulation of magnetic properties to electronic changes brought about by the binding of the molecules to the semiconductor surface. © 2003 American Institute of Physics.
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75.70.Rf Surface magnetism
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.43.Fg Adsorbate structure (binding sites, geometry)

Very low chemical disorder in epitaxial NiMnSb films on GaAs(111)B

W. Van Roy, M. Wójcik, E. Jędryka, S. Nadolski, D. Jalabert, B. Brijs, G. Borghs, and J. De Boeck

Appl. Phys. Lett. 83, 4214 (2003); http://dx.doi.org/10.1063/1.1627938 (3 pages) | Cited 20 times

Online Publication Date: 12 November 2003

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Single-crystalline NiMnSb(111) films with negligibly low defect levels have been grown epitaxially on GaAs(111)B using molecular beam epitaxy and characterized by nuclear magnetic resonance. In a film with only 1% deviation from stoichiometry, 1.1% of all Mn atoms is involved in planar defects, ∼ 0.5% of all Sb sites is occupied by AsSb substitutional atoms, and ∼ 0.2% of all Sb atoms has a modified environment. Both the average concentration of defects and the interface orientation are compatible with maintaining a half-metallic band structure at the ferromagnet/semiconductor interface, making these films a good candidate for spin injection into a semiconductor. © 2003 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.40.Ns Metal-nonmetal contacts
75.50.Cc Other ferromagnetic metals and alloys
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
76.60.-k Nuclear magnetic resonance and relaxation
61.66.Dk Alloys

Narrow commensurate states induced by a periodic array of nanoscale antidots in Nb superconductor

A. A. Zhukov, P. A. J. de Groot, V. V. Metlushko, and B. Ilic

Appl. Phys. Lett. 83, 4217 (2003); http://dx.doi.org/10.1063/1.1627478 (3 pages) | Cited 10 times

Online Publication Date: 12 November 2003

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We examine the interactions of the vortex lattice with a periodic square array of holes in a superconducting Nb film. Using high-resolution magnetic-field measurements of electrical losses, extremely narrow states with a magnetic field width reaching 1% of the matching field value are found at the commensurate points. They are accompanied by pronounced harmonic generation in response to ac modulation of the magnetic field or current. We relate these sharp anomalies to a locked commensurate state with characteristics of a Mott insulator. This offers opportunities for applications of superconducting films with periodic hole arrays as sensitive magnetic field detectors. © 2003 American Institute of Physics.
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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)
74.78.-w Superconducting films and low-dimensional structures
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
74.25.Jb Electronic structure (photoemission, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena
07.55.Ge Magnetometers for magnetic field measurements
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Enhancement of Curie temperature in Ga1−xMnxAs/Ga1−yAlyAs ferromagnetic heterostructures by Be modulation doping

T. Wojtowicz, W. L. Lim, X. Liu, M. Dobrowolska, J. K. Furdyna, K. M. Yu, W. Walukiewicz, I. Vurgaftman, and J. R. Meyer

Appl. Phys. Lett. 83, 4220 (2003); http://dx.doi.org/10.1063/1.1628815 (3 pages) | Cited 39 times

Online Publication Date: 12 November 2003

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The effect of modulation doping by Be on the ferromagnetic properties of Ga1−xMnxAs is investigated in Ga1−xMnxAs/Ga1−yAlyAs heterojunctions and quantum wells. Introducing Be acceptors into the Ga1−yAlyAs barriers leads to an increase of the Curie temperature TC of Ga1−xMnxAs, from 70 K in undoped structures to over 100 K with the modulation doping. This increase is qualitatively consistent with a multiband mean field theory simulation of carrier-mediated ferromagnetism. An important feature is that the increase of TC occurs only in those structures where the modulation doping is introduced after the deposition of the magnetic layer, but not when the Be-doped layer is grown first. This behavior is expected from the strong sensitivity of Mn interstitial formation to the value of the Fermi energy during growth. © 2003 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.J- Point defects and defect clusters
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.55.Eq III-V semiconductors
75.50.Dd Nonmetallic ferromagnetic materials

Reversible axial-strain effect and extended strain limits in Y-Ba-Cu-O coatings on deformation-textured substrates

N. Cheggour, J. W. Ekin, C. C. Clickner, D. T. Verebelyi, C. L. H. Thieme, R. Feenstra, and A. Goyal

Appl. Phys. Lett. 83, 4223 (2003); http://dx.doi.org/10.1063/1.1628818 (3 pages) | Cited 48 times

Online Publication Date: 12 November 2003

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The dependence of transport critical-current density Jc on axial tensile strain ε was measured at 76 K and self-magnetic field for YBa2Cu3O7−δ (YBCO) coatings on buffered, deformation-textured substrates of pure Ni, Ni–5-at. %-W, and Ni–10-at. %-Cr–2-at. %-W. Expectations have been that the strain tolerance of these composites would be limited by the relatively low yield strains of the deformation-textured substrates, typically less than 0.2%. However, results show that the irreversible degradation of Jc(ε) occurs at a strain equal to about twice the yield strain of the substrate. Therefore, YBCO/Ni-alloy composites may satisfy axial-strain performance requirements for electric devices, including the most demanding applications, motors and generators in which a strain tolerance exceeding 0.25% is needed. Furthermore, the YBCO/Ni–5-at. %-W conductors showed a reversible strain effect, which may be induced by a reversible strain-field broadening around mismatch dislocations at the grain boundaries. This effect may contribute to the unexpectedly large usable strain range of these conductors. © 2003 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
61.72.Mm Grain and twin boundaries
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