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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 336-342 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Current–voltage characteristics of single- and polycrystalline organic field-effect transistors are analyzed. The effect of bulk, interface, and grain boundary traps is investigated. The frequently observed dependence of the field-effect mobility on the gate voltage is ascribed to trapping processes rather than to an intrinsic charge transport mechanism in these organic semiconductors. Furthermore, the thermally activated mobility in polycrystalline devices, frequently observed, is ascribed to the formation of a potential barrier at the grain boundaries of the polycrystalline semiconductor. The barrier height depends significantly on the trap density and the position of the Fermi energy and therefore on the gate voltage. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed study of doped LaMnO3 with fixed carrier concentration has revealed a direct relationship between the Curie temperature Tc and the average ionic radius of the La site 〈rA〉, which is varied by substituting rare earths of different ionic radii for La. With decreasing 〈rA〉 magnetic order and significant magnetoresistance occur at lower temperatures with increasing temperature hysteresis, and the magnitude of the magnetoresistance increases dramatically. The predominant structural effect of decreasing 〈rA〉 is to decrease the Mn–O–Mn bond angle, which is accompanied by slight variations in the Mn–O bond distance. These results demonstrate that the notion of "double exchange'' must be generalized to include changes in the Mn–Mn electronic hopping element as a result of microstructural changes induced by composition, temperature and pressure variations. © 1996 American Institute of Physics.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on small angle neutron scattering studies of the flux-line lattice in single crystal 2H-NbSe2. For fields inclined with respect to the c axis, we find distortions and form factors consistent with Ginzburg–Landau corrections to the London equations with a mass anisotropy Γ=10.1±0.9. The flux lattice orientation, however, remains pinned to the crystal lattice for all tilts studied, in disagreement with the orientation defined by anisotropic London theory. For fields below 2 kG parallel to the c axis, the peaks are no longer resolution limited. The correlation lengths extracted are history dependent, and show that the lattice is annealed when a current greater than the critical current is applied. This occurs both when a direct transport current is used, or an induced current in a zero field cooled experiment. The annealing is seen in both the transverse and longitudinal correlation lengths, and calls into question the relationship between the Larkin–Ovchinnikov correlation length and the measured critical currents in this system.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4953-4953 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated and studied the structure and magnetic properties of high quality single crystalline (La0.7Ca0.3)MnO3 and (La0.7Ba0.3)MnO3 films. Films were grown on SrTiO3 as well as LaAlO3 substrates. (La0.7Ca0.3)MnO3 and (La0.7Ba0.3)MnO3 films grown on SrTiO3 exhibit excellent crystallinity and magnetic properties while those grown on LaAlO3 show mediocre structural and magnetic properties. These differences indicate the importance of lattice match and structural similarity between the film and the substrate. X-ray and Rutherford backscattering analysis provide a consistent picture of the structural properties of these doped manganite films. These films enable us to investigate the crystal anisotropy using vibrating sample magnetometry and torque magnetometry. Multilayers composed of manganite layers with different dopants (e.g., calcium and barium dopants) also have excellent structural properties since there is minimal strain at the interfaces. Such isostructural single crystalline multilayers are essential for investigating exchange coupling of the doped manganites.© 1997 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3904-3906 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear microwave response of superconducting YBa2Cu3O7−δ thin films and crystals was studied quantitatively by measuring the third-order harmonic amplitude E3ω (ω: 35 GHz, jRF≤3×104 A/cm2). We find E3ω to be dominated by two extrinsic effects: (1) the interaction with flux lines in weak links, leading to an increased nonlinear response at low temperatures, and (2) rf related flux line creation at film edges, yielding a high E3ω-signal close to Tc. Both effects together lead to a minimum in E3ω around 40–60 K, which makes this temperature interval interesting for rf applications. Intrinsic nonlinearities are smaller by orders of magnitude and could not be detected. © 1997 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3494-3496 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report significant improvement in the magnetoresistive (MR) response of perovskite manganites for small applied fields by the use of heterostructures with soft ferromagnets. At room temperature, a 5900-fold enhancement of the MR response at 10 Oe in La2/3Ca1/3MnO3 has been achieved using (Mn,Zn)Fe2O4 as the soft ferromagnet. By utilizing soft ferromagnets with various magnetic properties, this technique allows for enormous flexibility in "designing'' a desired MR response for the manganites, particularly in low fields. © 1996 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 763-765 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the resistance below Tc of single crystals of the high-temperature superconductors Ba2YCu3O7 and Bi2.2Sr2Ca0.8Cu2O8+δ in magnetic fields up to 12 T. The resistive transition of both compounds is dominated by intrinsic dissipation which is thermally activated, resulting in an exponential temperature dependence of the resistivity well below Tc. The dissipation is significantly larger and of different character in the Bi-Cu compound than in Ba2YCu3O7. The relation between the activated behavior and the depinning critical current is discussed.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3189-3190 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the low-temperature susceptibility and specific heat of the compound UIrGe and find both an antiferromagnetic phase transition at 16 K and a high-temperature electronic specific heat coefficient of 145 mJ/mole K2. Comparison of this behavior is made with other heavy fermion magnetic systems and a monotonic relationship is found between TN and the difference in the electronic specific heat coefficient γ above and below the transition.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 4237-4239 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: SmMn2Ge2 shows reentrant ferromagnetism. Using flux grown single crystals we find that on cooling through the Curie temperature (Tt1=350 K) the material becomes ferromagnetic (FM). Upon further cooling, at Tt2=150 K an antiferromagnetic (AFM) phase is reached which is stable until Tt3=100 K when there is a transition to FM. The transitions at Tt1 and Tt2 are first order with a temperature hysteresis of about 4 K. Using ac susceptibility to determine the various transition temperatures as a function of pressure (P) we find that Tt3 rapidly decreases with increasing P and at relatively low pressures falls below our measuring range (90 K). Tt2 increases nearly linearly with P and reaches 330 K and 11 kbar. Tt1, drops slowly with increasing P and at 11 kbar the high temperature FM region ends. An x-ray determination of the lattice parameters (at atm pressure) shows that in the AFM region the a0 lattice parameter is decreased, discontinuously changing at Tt2 and Tt3. The c0 lattice parameter is essentially unchanged going through this transition region. These observations indicate that the magnetic properties of SmMn2Ge2 are very sensitive to interatomic spacing. Measurements with a differential scanning calorimeter show that, on heating, the transition at Tt2 is endothermic.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 459-461 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An experimental technique is described which employs resistive strain gauges to measure the pressure–volume relationship of solids up to∼50 kbar. The strain resolution is better than 10 ppm with a dynamical range up to 20 000. Two examples are presented to illustrate the sensitivity and the reliability of this technique.
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