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25 Mar 2002

Volume 80, Issue 12, pp. 2045-2227

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Magnesium-diboride ramp-type Josephson junctions

Dragana Mijatovic, Alexander Brinkman, Ingrid Oomen, Guus Rijnders, Hans Hilgenkamp, Horst Rogalla, and Dave H. A. Blank

Appl. Phys. Lett. 80, 2141 (2002); http://dx.doi.org/10.1063/1.1462869 (3 pages) | Cited 36 times

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Josephson junctions have been realized in which two superconducting magnesium-diboride (MgB2) layers are separated by a thin MgO barrier layer, using the ramp-type configuration. Their current–voltage characteristics follow the behavior described by the resistively shunted junction model, with an excess current of about 30% of the critical current Ic. A suppression of 70% of Ic was achieved in applied magnetic fields. Shapiro steps were observed by irradiating the junctions with 10.0 GHz microwaves, and the dependence of the step height on applied rf current is well described by a current–source model. Reference samples prepared without the MgO layer showed strong-link behavior with large Ic values. © 2002 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
85.25.Cp Josephson devices
74.25.N- Response to electromagnetic fields

Spin hopping in a discontinuous La0.7Ca0.3MnO3 film

Michael Ziese

Appl. Phys. Lett. 80, 2144 (2002); http://dx.doi.org/10.1063/1.1462870 (3 pages) | Cited 14 times

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Magnetization and magnetotransport properties of a discontinuous La0.7Ca0.3MnO3 film on LaAlO3 are presented. The sample shows transport characteristics of a granular ferromagnet with an extraordinarily large magnetoresistance. The data are successfully interpreted within a model of spin-dependent tunneling between grains taking into account magnetic intergrain correlation effects. © 2002 American Institute of Physics.
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73.61.Ng Insulators
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.50.Dd Nonmetallic ferromagnetic materials
75.45.+j Macroscopic quantum phenomena in magnetic systems
75.47.De Giant magnetoresistance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Reduction of ordering temperature of an FePt-ordered alloy by addition of Cu

Tomoyuki Maeda, Tadashi Kai, Akira Kikitsu, Toshihiko Nagase, and Jun-ichi Akiyama

Appl. Phys. Lett. 80, 2147 (2002); http://dx.doi.org/10.1063/1.1463213 (3 pages) | Cited 166 times

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We have found that the addition of Cu to an FePt alloy film is an effective approach for reducing the ordering temperature of FePt. The coercivity of the FePtCu film is around 5 kOe after annealing at 300 °C, whereas that of FePt shows several hundred Oe. In the FePtCu film annealed at 700 °C, the coercivity is almost the same as for the FePt films. Therefore, the FePtCu film displays a hard-magnetic property similar to that of the FePt film. The results of x-ray diffraction indicate that a ternary FePtCu alloy is formed. Thus, the formation of the ternary FePtCu alloy is considered to play an important role in reducing the ordering temperature. © 2002 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.-a Thin film structure and morphology
75.50.Bb Fe and its alloys
61.72.Cc Kinetics of defect formation and annealing
75.50.Ww Permanent magnets
68.55.Nq Composition and phase identification
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