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15 Apr 2002

Volume 80, Issue 15, pp. 2625-2806

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Hysteresis curves and self-field alternating-current losses in superconducting tapes with transport current: Edge barrier effect

I. L. Maksimov and A. A. Elistratov

Appl. Phys. Lett. 80, 2701 (2002); http://dx.doi.org/10.1063/1.1458691 (3 pages) | Cited 3 times

Online Publication Date: 10 April 2002

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The combined influence of both bulk pinning and edge barrier on zero-field transport properties and alternating-current (ac) losses in superconducting tapes and films is considered. The equilibrium distributions of the magnetic flux density n(y) and of the sheet current density i(y) are found analytically for the tapes with an oscillating transport current. The critical current is calculated taking into account both bulk and edge pinning of the magnetic flux, and the dependence of the dissipation loss power upon the ac amplitude I0 is found. The crossover from barrier- to pinning-controlled ac losses is predicted with the increase of current oscillation amplitude I0. © 2002 American Institute of Physics.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
84.71.Mn Superconducting wires, fibers, and tapes
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena

Thermodynamic calculations of the effect of B and Ta on magnetically induced phase separation in Co–Cr–Pt alloys

K. Oikawa, G. W. Qin, S. Okamoto, O. Kitakami, Y. Shimada, K. Fukamichi, and K. Ishida

Appl. Phys. Lett. 80, 2704 (2002); http://dx.doi.org/10.1063/1.1469684 (3 pages) | Cited 6 times

Online Publication Date: 10 April 2002

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In order to clarify the relation between the magnetically induced phase separation and the recording media characteristics, the thermodynamic calculations of Co–Cr–Pt–B and Co–Cr–Pt–Ta systems have been carried out by using the available binary assessment data and Miedema’s semiempirical values. B is segregated to the boundary in a similar manner as Cr, which makes the boundary region paramagnetic. This result is consistent with available data that B weakens the intergranular magnetic coupling and increases the magnetic anisotropy in Co–Cr–Pt recording media. By adding Ta, the Cr content in the paramagnetic phase is also increased, reducing the intergranular magnetic coupling. However, the Ta content in the ferromagnetic phase is higher than in the paramagnetic phase, decreasing the magnetic anisotropy. Accordingly, the thermodynamic calculations successfully explain experimental magnetic data for Co–Cr–Pt–B and Co–Cr–Pt–Ta recording media. © 2002 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.50.Cc Other ferromagnetic metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
64.75.-g Phase equilibria
65.40.G- Other thermodynamical quantities
75.30.Gw Magnetic anisotropy
75.20.Ck Nonmetals

Oxygen-deficiency-activated phase transition in a long-aged La0.8Ca0.2MnO3 film

V. G. Prokhorov, G. G. Kaminsky, V. A. Komashko, Y. P. Lee, J. S. Park, and H. C. Ri

Appl. Phys. Lett. 80, 2707 (2002); http://dx.doi.org/10.1063/1.1470244 (3 pages) | Cited 10 times

Online Publication Date: 10 April 2002

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The magnetic and transport properties of as-deposited and long-aged La0.8Ca0.2MnO3−δ films have been investigated in a wide temperature range. The x-ray diffraction data have shown separation of the film into two crystalline phases of the cubic and rhombohedral symmetry with different oxygen contents of δ ≃ 0.08 and 0.16, respectively, after a half-year aging at room temperature in air. Both phases testify two different electronic (metal–insulator) and magnetic transitions with similar maximum values of magnetoresistance. The possible mechanism for such a type of structural transition in the aged manganite thin films is discussed. © 2002 American Institute of Physics.
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68.55.Nq Composition and phase identification
75.47.De Giant magnetoresistance
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.30.+h Metal-insulator transitions and other electronic transitions
64.70.K- Solid-solid transitions

All solution-chemistry approach for YBa2Cu3O7−δ-coated conductors

M. P. Siegal, P. G. Clem, J. T. Dawley, R. J. Ong, M. A. Rodriguez, and D. L. Overmyer

Appl. Phys. Lett. 80, 2710 (2002); http://dx.doi.org/10.1063/1.1470225 (3 pages) | Cited 46 times

Online Publication Date: 10 April 2002

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A need exists for low-cost coated-conductor fabrication methods for applications in magnet and electric-power technologies. We demonstrate high-critical current density (Jc) YBa2Cu3O7−δ (YBCO) films grown on Nb-doped SrTiO3 (Nb:STO) buffered Ni(100) tapes. All buffer and superconductor layers are deposited using solution chemistry. A 50 nm thick Nb:STO seed layer on Ni(100) acts as a template for the growth of subsequent thicker layers of Nb:STO. Nb doping improves the electrical conductivity and oxygen diffusion barrier properties of STO. YBCO grows heteroepitaxially directly on this buffer layer, resulting in a transport Jc(77 K) = 1.3 MA/cm2. © 2002 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.72.-h Cuprate superconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Scanning magnetoresistance microscopy with a magnetoresistive sensor cantilever

Motonori Nakamura, Michiya Kimura, Kazuhisa Sueoka, and Koichi Mukasa

Appl. Phys. Lett. 80, 2713 (2002); http://dx.doi.org/10.1063/1.1469681 (3 pages) | Cited 10 times

Online Publication Date: 10 April 2002

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In this work, a cantilever with a magnetoresistive (MR) sensor is fabricated for scanning magnetoresistance microscope, in order to realize the simultaneous imaging of surface topography and stray magnetic field distribution. A constant current flowing through a meander-patterned metal wire produces a defined magnetic field, and the wire is used as a sample to demonstrate the simultaneous imaging and to reveal the field sensitivity of the cantilever. A MR image has been successfully obtained with lateral spatial resolution of a few μm and a field sensitivity (Hmin ≈ 1.7 Oe) at room temperature. © 2002 American Institute of Physics.
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07.79.Lh Atomic force microscopes
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.55.Ge Magnetometers for magnetic field measurements
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Low-temperature growth of NiMnSb thin films by pulsed-laser deposition

J. Giapintzakis, C. Grigorescu, A. Klini, A. Manousaki, V. Zorba, J. Androulakis, Z. Viskadourakis, and C. Fotakis

Appl. Phys. Lett. 80, 2716 (2002); http://dx.doi.org/10.1063/1.1469211 (3 pages) | Cited 17 times

Online Publication Date: 10 April 2002

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We report the growth of thin films of the ferromagnetic half-Heusler alloy NiMnSb by pulsed-laser deposition on Si (111) and polycrystalline InAs substrates. Highly crystalline films are grown using low substrate temperatures (190–210 °C), without any postdeposition annealing. The structural, magnetic, and transport properties of the films are relatively consistent with those of the bulk NiMnSb used as target, which suggests that thin layers of this material grown by laser ablation could be used in multilayer structures as effective spin-polarized conducting layers. © 2002 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
75.50.Cc Other ferromagnetic metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology

Improved thermal stability of synthetic ferrimagnetic media with enhanced exchange coupling strength

A. Inomata, E. N. Abarra, B. R. Acharya, A. Ajan, and I. Okamoto

Appl. Phys. Lett. 80, 2719 (2002); http://dx.doi.org/10.1063/1.1467696 (3 pages) | Cited 8 times

Online Publication Date: 10 April 2002

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The effect of the antiferromagnetic interlayer exchange coupling strength J between the initial or stabilization magnetic layer L1 and the top magnetic layer L2 on the thermal stability of synthetic ferrimagnetic media (SFM) is investigated. Enhanced J is achieved by the insertion of a thin Co-rich hexagonal close-packed layer between the Ru layer and L1, and such a structure did not change the read/write properties significantly. The contribution of the anisotropy energy of L1 to the thermal stability of SFM is improved by increasing J. However, a significant increase in the contribution of L1 to the thermal stability is achieved at relatively low J values (0.14 erg/cm2) which translate into only a 3–4% increase in the switching field H0. © 2002 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
75.50.Gg Ferrimagnetics
68.60.Dv Thermal stability; thermal effects
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetization reversal probed by spin-polarized tunneling

Moon-Ho Jo, N. D. Mathur, and M. G. Blamire

Appl. Phys. Lett. 80, 2722 (2002); http://dx.doi.org/10.1063/1.1469678 (3 pages) | Cited 10 times

Online Publication Date: 10 April 2002

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We report magnetic reversal processes in the magnetic tunnel junction (MTJ) based on a half metallic manganite, La0.7Ca0.3MnO3 by comprehensive spin-polarized tunneling (SPT) measurements. The large tunnel magnetoresistance up to 77% of (Rap−Rp)/Rap in the present MTJ is highly sensitive to the local magnetization fluctuation in the ferromagnetic electrodes and thus enables us to establish an instantaneous one-to-one correlation between the magnetization reversal and the SPT with the two-dimensional SPT measurements. We have found the systematic angular variations of the SPT features in the resistance-field curves, and based on the observed angular dependences, we propose a crucial role of the edge-domain pinning and the resultant multi-domain breakup for the magnetization reversal. © 2002 American Institute of Physics.
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85.75.Mm Spin polarized resonant tunnel junctions
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
75.47.De Giant magnetoresistance
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Improved superconducting properties in nanocrystalline bulk MgB2

A. Gümbel, J. Eckert, G. Fuchs, K. Nenkov, K.-H. Müller, and L. Schultz

Appl. Phys. Lett. 80, 2725 (2002); http://dx.doi.org/10.1063/1.1469654 (3 pages) | Cited 98 times

Online Publication Date: 10 April 2002

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High density nanocrystalline MgB2 bulk superconductors with distinctly improved pinning were prepared by mechanical alloying of Mg and B powders at ambient temperatures followed by hot pressing. The nanocrystalline samples reveal high jc = 105 A/cm2 at 20 K and 1 T together with an irreversibility line strongly shifted towards higher fields resulting in Hirr(T) ∼ 0.8 Hc2(T), whereas typically Hirr(T) ∼ 0.5 Hc2(T) is observed for untextured bulk samples. These values exceed those of all other reported bulk samples and are in the range of values for thin films. The improved pinning of this material, which mainly consists of spherical grains about 40–100 nm in size, is attributed to the large number of grain boundaries in the nanocrystalline state. © 2002 American Institute of Physics.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
74.25.Sv Critical currents
74.72.-h Cuprate superconductors
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.07.Wx Nanopowders
61.72.Mm Grain and twin boundaries
74.25.Ha Magnetic properties including vortex structures and related phenomena
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