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14 Jun 1999

Volume 74, Issue 24, pp. 3595-3737

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Exchange-biased magnetic tunnel junctions: Dependence of offset field on junction width

K.-S. Moon, R. E. Fontana, and S. S. P. Parkin

Appl. Phys. Lett. 74, 3690 (1999); http://dx.doi.org/10.1063/1.123222 (3 pages) | Cited 20 times

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Magnetic tunnel junction structures comprising a ferromagnetic layer pinned by exchange biasing and a “free” ferromagnetic layer were prepared using dc-magnetron sputtering and patterned with conventional optical lithography. Structures were prepared, square and rectangular in shape, with various widths and lengths. It was observed that the magnetic properties of the free layer vary systematically with the size of the junction. In particular, the offset field of the free-layer magnetic hysteresis loop, as measured resistively, is controlled by a combination of magnetostatic and ferromagnetic coupling between the pinned and free layers. © 1999 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
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
75.45.+j Macroscopic quantum phenomena in magnetic systems
81.15.Cd Deposition by sputtering

Microwave-induced current steps in intrinsic Josephson junctions patterned on Bi2Sr2CaCu2O8 single crystal

H. B. Wang, Y. Aruga, T. Tachiki, Y. Mizugaki, J. Chen, K. Nakajima, T. Yamashita, and P. H. Wu

Appl. Phys. Lett. 74, 3693 (1999); http://dx.doi.org/10.1063/1.123223 (3 pages) | Cited 13 times

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With a 10 μm×10 μm mesa patterned on Bi2Sr2CaCu2O8 single crystals, we measure the current–voltage (I–V) curves of a stack of intrinsic Josephson junctions. Current steps are observed at an equal voltage spacing of 4 mV when the sample is subjected to microwave radiation at around 7 GHz. With increase of the microwave power, more steps occur while the spacing between neighboring steps does not seem to change. The magnitude of each step depends on the microwave power in an oscillating way. Tuning the microwave frequency causes such steps to occur over separate frequency ranges, and each range is quite narrow. A temperature rise from 4.2 to 14.3 K completely quenches the step structures. Possible explanations for the step structures, based on resonances excited by microwave or geometric resonances in the junction cavity, are discussed. © 1999 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors
74.25.F- Transport properties
74.25.N- Response to electromagnetic fields

Pulsed-laser-deposited epitaxial Sr2FeMoO6−y thin films: Positive and negative magnetoresistance regimes

H. Asano, S. B. Ogale, J. Garrison, A. Orozco, Y. H. Li, E. Li, V. Smolyaninova, C. Galley, M. Downes, M. Rajeswari, R. Ramesh, and T. Venkatesan

Appl. Phys. Lett. 74, 3696 (1999); http://dx.doi.org/10.1063/1.123224 (3 pages) | Cited 49 times

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Epitaxial thin films of ordered double-perovskite Sr2FeMoO6−y are deposited on (001) SrTiO3 substrates by pulsed-laser deposition using a two step growth process. Selection of growth conditions is found to lead to either highly conductive metallic thin films (residual resistivity of about 1 μΩ cm) or semiconducting films. The metallic films show a positive magnetoresistance (MR) as high as 35%, while the semiconducting films show a negative MR of −3%, at a temperature of 5 K and a field of 8 T. © 1999 American Institute of Physics.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Le Other inorganic semiconductors
73.61.At Metal and metallic alloys

Quantum constraints on technological superconductors

J. R. Thompson, J. G. Ossandon, L. Krusin-Elbaum, K. J. Song, D. K. Christen, and J. L. Ullmann

Appl. Phys. Lett. 74, 3699 (1999); http://dx.doi.org/10.1063/1.123225 (3 pages) | Cited 5 times

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Vortex pinning in textured Bi2Sr2CaCu2Ox/Ag superconducting tapes was enhanced by irradiation with 0.8 GeV protons, creating randomly oriented columnar defects. Measurements of the current density J versus time show that thermally-activated current decay was greatly decreased, compared with unirradiated tapes. However, temperature-independent quantum tunneling of vortices considerably limits J and its temporal stability, for a significant fraction of the finite-Jc region. © 1999 American Institute of Physics.
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84.71.Mn Superconducting wires, fibers, and tapes
74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
61.80.Jh Ion radiation effects
61.82.-d Radiation effects on specific materials
61.72.-y Defects and impurities in crystals; microstructure

Magnetic field biasing in Faraday effect sensors

H. Guerrero, R. Pérez del Real, R. Fernández de Caleya, and G. Rosa

Appl. Phys. Lett. 74, 3702 (1999); http://dx.doi.org/10.1063/1.123226 (3 pages) | Cited 2 times

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A method for improving the performances of Faraday effect sensors, which is based in the passive magnetic field biasing of a Faraday rotator, is described. It allows obtaining reflective optical fiber sensor architectures, based on a single polarizer and a mirror-coated Faraday rotator, which exhibit linear response and maximum sensitivity. It can be achieved by means of a permanent magnet providing a 45° rotation of the polarization of the optical beam propagating through a Faraday rotator. Operation of this method in both a point magnetic field sensor and a current sensor, with a ferromagnetic ring as concentrator, has been demonstrated. © 1999 American Institute of Physics.
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42.81.Pa Sensors, gyros
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.70.Sq Magnetooptical devices
07.60.Vg Fiber-optic instruments
07.55.Ge Magnetometers for magnetic field measurements
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
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