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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Suppression of superconductivity due to spin imbalance in Co/Al/Co single electron transistor

Jan Johansson, Mattias Urech, David Haviland, and V. Korenivski

J. Appl. Phys. 93, 8650 (2003); http://dx.doi.org/10.1063/1.1556284 (3 pages) | Cited 15 times

Online Publication Date: 9 May 2003

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Transport properties of ferromagnetic/nonmagnetic/ferromagnetic single electron transistors are investigated as a function of external magnetic-field, temperature, bias, and gate voltage. By designing the magnetic electrodes to have different switching fields, a two-mode device is realized having two stable magnetization states, with the electrodes aligned in parallel and antiparallel. Magnetoresistance of approximately 100% is measured in Co/AlOX/Al/AlOX/Co double tunnel junction spin valves at low bias, with the Al spacer in the superconducting state. The effect is substantially reduced at high bias and temperatures above the TC of the Al. The experimental results are interpreted as due to spin imbalance of charge carriers resulting in suppression of the superconducting gap of the Al island. © 2003 American Institute of Physics.
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85.35.Gv Single electron devices
85.25.Cp Josephson devices
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Synthesis and properties of hole-doped Li1−xBC

L. Zhao, P. Klavins, and Kai Liu

J. Appl. Phys. 93, 8653 (2003); http://dx.doi.org/10.1063/1.1556285 (3 pages) | Cited 12 times

Online Publication Date: 9 May 2003

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Stoichiometric LiBC has been synthesized using both arc melting and sealed tantalum ampoule methods. Hole-doped Li1−xBC (0<x⩽0.37) compounds have been realized through vacuum deintercalation from LiBC. The hexagonal crystal lattice has remained largely intact, with only slight decreases in lattice parameters upon hole-doping. The samples are intrinsically diamagnetic and are semiconducting in the 2–300 K range studied. Increased hole-doping leads to a color darkening as well as a decrease in resistivity. © 2003 American Institute of Physics.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.05.Hd Other semiconductors
75.20.Ck Nonmetals
72.20.Fr Low-field transport and mobility; piezoresistance
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.66.Fn Inorganic compounds

Magnetic properties and superconductivity of mechanically alloyed (Mg1−xFex)B2 samples with x=0.0–0.4

Y. D. Gao, J. Ding, G. V. S. Rao, and B. V. R. Chowdari

J. Appl. Phys. 93, 8656 (2003); http://dx.doi.org/10.1063/1.1556286 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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In the current work, we have prepared and studied (Mg1−xFex)B2 samples with x=0.0–0.4 prepared by mechanical alloying and subsequent vacuum annealing. All the as-milled powders were found to be amorphous in x-ray diffraction examination and no superconductivity was evident until 4.2 K. The MgB2 phase was formed after a vacuum annealing at 450 °C or higher. For the pure MgB2 sample without Fe substitution, critical temperatures of 38–39 K was measured for the samples after heat treatment at 450 °C or higher. For Fe-containing samples (Mg1−xFex)B2 with x=0.05–0.2, the solubility of Fe in the MgB2 phase decreased with increasing annealing temperature as confirmed by x-ray diffraction and Mössbauer studies. Besides MgB2, other phases (α-Fe, Fe2B, and MgB4) were observed. The critical temperature Tc increased with increasing annealing temperatures, indicating that Tc decreased with increasing Fe concentration in the MgB2 phase. For (Mg0.6Fe0.4)B2, the MgB2 phase could not be formed after heat treatment and MgB4 and Fe2B were the major phases after crystallization. Superconductivity was not observed in the as-milled and subsequently annealed (Mg0.6Fe0.4)B2 specimens. © 2003 American Institute of Physics.
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74.10.+v Occurrence, potential candidates
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.40.Rs Electrical and magnetic properties related to treatment conditions
76.80.+y Mössbauer effect; other γ-ray spectroscopy
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Time evolution of the second magnetization peak in Bi2Sr2CaCu2O8+δ

B. Kalisky, A. Shaulov, T. Tamegai, and Y. Yeshurun

J. Appl. Phys. 93, 8659 (2003); http://dx.doi.org/10.1063/1.1556287 (3 pages) | Cited 6 times

Online Publication Date: 9 May 2003

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Local magnetization curves at different times, extracted from high-temporal resolution magneto-optical measurements in Bi2Sr2CaCu2O8+δ, demonstrate the absence of the second magnetization peak at short times, its appearance at longer times, and the movement of its onset toward higher-induction fields approaching the thermodynamic vortex order–disorder transition field. We relate this phenomena to metastable disordered states induced by edge contamination for inductions in the vicinity of the order–disorder vortex phase transition. We show that the time evolution of the second magnetization peak is governed by the relaxation times of the metastable disordered vortex states. © 2003 American Institute of Physics.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.72.-h Cuprate superconductors
78.20.Ls Magneto-optical effects
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Interplay of superconductivity and magnetism in the single crystals of Er1−xTbxNi2B2C

B. K. Cho, C. A. Kim, and H.- C. Ri

J. Appl. Phys. 93, 8662 (2003); http://dx.doi.org/10.1063/1.1556288 (3 pages)

Online Publication Date: 9 May 2003

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The measurements of temperature-dependent resistivity ρ(T) and magnetization M(T) are carried out for the single crystals of Er1−xTbxNi2B2C (x=0.0, 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.6, 0.7, 0.8, 0.9, and 1.0) in order to study the superconductivity, magnetism, and their interplay in the temperature range of 2 K⩽T⩽20 K. From the analysis of the ρ(T) and M(T) data, the superconducting (Tc), antiferromagnetic (TN), and weak ferromagnetic (TWF), transition temperatures are derived and represented in terms of De Gennes (DG) factor. It is found that the Tc is suppressed with increasing Tb concentration and a crossover for Tc<TN occurs at x=0.2. Tc variation follows well the DG scaling even when Tc<TN. The TN is almost independent of temperature at T≈6 K in the Er-rich side of the compounds (x⩽0.4) and follows DG scaling based on the Ruderman–Kittel–Kasuya–Yosida interaction in Tb-rich side (x⩾0.6). The TWF also shows distinct behaviors in a Er- and Tb-rich region. The observed superconductivity, AF-ordered state, and weak ferromagnetic state are found to be closely correlated and will be discussed based on the magnetic interactions between Er and Tb elements. © 2003 American Institute of Physics.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.25.Ha Magnetic properties including vortex structures and related phenomena
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
74.25.F- Transport properties
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics

Periodic orbit resonance in (TMTSF)2ClO4

A. E. Kovalev, S. Hill, S. Takahashi, T. N. Dhakal, S. Takasaki, J. Yamada, H. Anzai, and J. S. Brooks

J. Appl. Phys. 93, 8665 (2003); http://dx.doi.org/10.1063/1.1556289 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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We have studied the magnetoelectrodynamics of the layered molecular conductor (TMTSF)2ClO4 at millimeter wave frequencies. The high-quality data were obtained in a split-pair magnet using a cavity perturbation technique. We found clear periodic orbit resonance due to the quasi-one-dimensional Fermi surface in the studied compound. These phenomena were investigated in detail. Using our data, we extracted a value for the Fermi velocity which is about 1.8×105 m/s. © 2003 American Institute of Physics.
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72.15.Nj Collective modes (e.g., in one-dimensional conductors)
71.20.Rv Polymers and organic compounds
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
74.70.Kn Organic superconductors
72.30.+q High-frequency effects; plasma effects
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