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31 Mar 2003

Volume 82, Issue 13, pp. 1999-2184

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Appl. Phys. Lett. 82, 2094 (2003); http://dx.doi.org/10.1063/1.1563813 (3 pages)

Y. J. Lee, J. von Boehm, M. Pesola, and R. M. Nieminen
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Superconducting MgB2 thin films on silicon carbide substrates by hybrid physical–chemical vapor deposition

X. H. Zeng, A. V. Pogrebnyakov, M. H. Zhu, J. E. Jones, X. X. Xi, S. Y. Xu, E. Wertz, Qi Li, J. M. Redwing, J. Lettieri, V. Vaithyanathan, D. G. Schlom, Zi-Kui Liu, O. Trithaveesak, and J. Schubert

Appl. Phys. Lett. 82, 2097 (2003); http://dx.doi.org/10.1063/1.1563840 (3 pages) | Cited 74 times

Online Publication Date: 25 March 2003

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We have used two polytypes of silicon carbide single crystals, 4H-SiC and 6H-SiC, as the substrates for MgB2 thin films grown by hybrid physical-chemical vapor deposition (HPCVD). The c-cut surface of both polytypes has a hexagonal lattice that matches closely with that of MgB2. Thermodynamic calculations indicate that SiC is chemically stable under the in situ deposition conditions for MgB2 using HPCVD. The MgB2 films on both polytypes show high-quality epitaxy with a Rutherford backscattering channeling yield of 12%. They have Tc above 40 K, low resistivities, high residual resistivity ratios, and high critical current densities. The results demonstrate that SiC is an ideal substrate for MgB2 thin films. © 2003 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
74.25.Sv Critical currents
74.10.+v Occurrence, potential candidates
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Magnetism in cobalt-doped Cu2O thin films without and with Al, V, or Zn codopants

S. N. Kale, S. B. Ogale, S. R. Shinde, M. Sahasrabuddhe, V. N. Kulkarni, R. L. Greene, and T. Venkatesan

Appl. Phys. Lett. 82, 2100 (2003); http://dx.doi.org/10.1063/1.1564864 (3 pages) | Cited 37 times

Online Publication Date: 25 March 2003

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Thin films of 5% Co doped Cu2O were grown on single-crystal (001) MgO substrates by pulsed-laser deposition, without and with 0.5% codoping with Al, V, or Zn. Structural, electrical, and magnetic properties were studied. The films showed phase-pure character under the chosen optimum growth conditions. Spin-glass-like behavior was observed in Co-doped films without codoping. A clear ferromagnetic signal at room temperature was found only in the case of Co:Cu2O films codoped with Al. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Lk Spin glasses and other random magnets
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
68.55.-a Thin film structure and morphology
73.61.Le Other inorganic semiconductors
75.40.-s Critical-point effects, specific heats, short-range order
81.05.Hd Other semiconductors

High critical-current density in robust MgB2/Mg nanocomposites

Qiang Li, G. D. Gu, and Y. Zhu

Appl. Phys. Lett. 82, 2103 (2003); http://dx.doi.org/10.1063/1.1564871 (3 pages) | Cited 17 times

Online Publication Date: 25 March 2003

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A robust and high critical-current density (Jc>1 MA/cm2 at 5 K and self-field) superconducting composite based on MgB2 has been developed. The composite consists of 75% MgB2 matrix and 25% dispersed Mg on the scale of tens of nanometers. Transmission electron microscope investigation revealed that the composites are extremely dense, and consist of nanosized MgB2 grains connected by the clean strongly coupled grain boundaries. The nanodispersed Mg can blunt crack tips and provides regions for plastic flow. Both magnetization and magneto-optical studies demonstrated that the composite is free of any weak links. Furthermore, the addition of Mg in the matrix substantially reduces the flux jumps commonly observed in the monolithic MgB2 superconductors. © 2003 American Institute of Physics.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Sv Critical currents
61.72.Mm Grain and twin boundaries
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
68.37.Lp Transmission electron microscopy (TEM)
74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation
74.25.Ha Magnetic properties including vortex structures and related phenomena
78.20.Ls Magneto-optical effects
74.25.Gz Optical properties

Variation of domain formation in a 15 nm NiFe layer exchange coupled with NiO layers of different thicknesses

Z. Y. Liu and S. Adenwalla

Appl. Phys. Lett. 82, 2106 (2003); http://dx.doi.org/10.1063/1.1564639 (3 pages) | Cited 12 times

Online Publication Date: 25 March 2003

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The correlation between ferromagnetic domain formation and exchange bias in a series of NiFe/NiO samples with varying NiO thicknesses has been investigated using the magneto-optic Kerr effect and magnetic force microscopy. Below a critical thickness (15 nm) of NiO, the exchange bias HE is zero and ripple domains exist in the NiFe layer. Above this critical thickness, cross-tie type domain walls appear concurrently with the appearance of exchange bias. Both the number of cross-tie domain walls and the exchange bias increase with an increase in NiO thickness, reaching a maximum at 35 nm NiO, after which both show a gradual decrease. This variation of domain wall formation in the NiFe layer with the NiO thickness possibly reflects the variation of the domain structure in the NiO layer through interfacial exchange coupling. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
78.20.Ls Magneto-optical effects
68.37.Rt Magnetic force microscopy (MFM)

Josephson device for simultaneous time and energy detection

E. Esposito, M. Ejrnaes, S. Pagano, D. Perez de Lara, and R. Cristiano

Appl. Phys. Lett. 82, 2109 (2003); http://dx.doi.org/10.1063/1.1564297 (3 pages) | Cited 3 times

Online Publication Date: 25 March 2003

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The development of a detection device for simultaneous measurement of energy and impact time, to be used in time-of-flight mass spectrometry, is reported. In this device, two superconducting tunnel junctions are coupled through a passive network. The first junction operates in the quasiparticle regime in order to measure the energy of a molecule impact and to act as a proportional detector. The second one operates in the Josephson regime in order to act as a fast discriminator for the impact time of a molecule impinging on the detector junction. In this way, a very accurate time determination can be achieved limited only by the intrinsic detector response, thus improving the spectrometer mass resolution. To demonstrate the feasibility of this detection scheme in mass spectrometry, calibration measurements have been carried out using a 55Fe x-ray source to simulate the molecule impact. The experimental results successfully demonstrated simultaneous detection of energy and arrival time in coincidence with photon impacts, with a time resolution limited, in practice, only by the electronics used. © 2003 American Institute of Physics.
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85.25.Cp Josephson devices
06.30.Ft Time and frequency
07.75.+h Mass spectrometers
06.20.F- Units and standards
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Damping as a function of pulsed field amplitude and bias field in thin film Permalloy

J. P. Nibarger, R. Lopusnik, and T. J. Silva

Appl. Phys. Lett. 82, 2112 (2003); http://dx.doi.org/10.1063/1.1564866 (3 pages) | Cited 29 times

Online Publication Date: 25 March 2003

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We have measured the step response in thin film Permalloy as a function of both a hard-axis pulsed field amplitude and an easy-axis longitudinal magnetic bias field using a pulsed inductive microwave magnetometer. The bias field ranged from 0 to 8000 A/m (0 to 100 Oe) and the pulsed field varied from 0.32 to 320 A/m (0.004 to 4 Oe). The rotation angle of the equilibrium magnetization direction varied from 0.002° to 40° for this range of field values. Data were analyzed to extract the Gilbert damping parameter, α. The damping parameter decreased monotonically with an increase in longitudinal bias field. However, there is no observed dependence of α on the pulse amplitude, indicating that the damping is independent of the angle of rotation. We conclude that there is no significant nonlinear generation of spin waves that affects the damping in the case of free induction decay for the range of field pulses employed. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Ds Spin waves
75.50.Bb Fe and its alloys
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Enhancement of the current in a superconductor strip by means of curved superconducting shields

Y. A. Genenko and H. Rauh

Appl. Phys. Lett. 82, 2115 (2003); http://dx.doi.org/10.1063/1.1560866 (3 pages) | Cited 3 times

Online Publication Date: 25 March 2003

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The distribution of the sheet current in a superconductor strip located between superconducting shields of various geometries is studied on the basis of exact analytic forms. Whereas the current becomes increasingly uniform when flat shields approach the strip, strong inhomogeneities are found to develop for curved shields, with concomitant enhancements by several times of the maximum total current predicted in the marginal Meissner state; a trait which could be favorably exploited regarding superconductor electronics applications. © 2003 American Institute of Physics.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
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