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  • 1
    ISSN: 1573-8663
    Schlagwort(e): manganites ; magnetoresistance ; lattice mismatch ; lanthanum manganate ; strain ; microwaves ; annealing
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Notizen: Abstract This paper examines the possibility of enhancing the room temperature magnetoresistance at low applied magnetic fields in single layer La0.7 Ba0.3 MnO3 thin films. The influence of lattice mismatch strain, as well as the effect of different frequency regimes, on the magnetoresistance is explored. The effects of lattice mismatch strain are studied by measuring the magnetoresistance as a function of the La0.7 Ba0.3 MnO3 film thickness, oxygen annealing, and lattice matched buffer layers. We find that the release of the lattice mismatch strain improves the magnetoresistance at room temperature and at low magnetic fields. In fact, the highest magnetoresistance at room temperature (−1.7% at 500 Oe) has been found for the 1600  Å as-grown La0.7 Ba0.3 MnO3 film, whereas the largest magnetoresistance (−1.9% at 500 Oe) is found at 309 K for the 1000  Å La0.7 Ba0.3 MnO3 film annealed in flowing O2 for 1 h at 900°C. Finally, we find that the microwave magnetoresistance is the same as the dc magnetoresistance when the cavity corrections are applied. In the single layer La0.7 Ba0.3 MnO3 system, the low field magnetoresistance at room temperature is far from being technologically viable.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    ISSN: 1572-9605
    Schlagwort(e): Superconductivity ; ac losses ; Y-Ba-Cu-O ; Tl-Ca-Ba-Cu-O
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract We have used a novel bolometric technique and a resonant technique to obtain accurate submillimeter and microwave residual loss data for epitaxial thin films of YBa2Cu3O7, Tl2Ca2Ba2Cu3O10, and Tl2CaBa2Cu2O8. For all films we obtain good agreement between the submillimeter and microwave data, with the residual losses in both the Y-Ba-Cu-O and Tl-Ca-Ba-Cu-O films scaling approximately as frequency squared below ∼1 THz. We are able to fit the losses in the Y-Ba-Cu-O films to a weakly coupled grain model for thea-b plane conductivity, in good agreement with results from a Kramers-Kronig analysis of the loss data. We observe strong phonon structure in the Tl-Ca-Ba-Cu-O films for frequencies between 2 and 21 THz, and are unable to fit these losses to the simple weakly coupled grain model. This is in strong contrast to the case for other high-T c superconductors such as YBa2Cu3O7, where phonon structure observed in ceramic samples is absent in epitaxial oriented films and crystals because of the electronic screening due to the high conductivity of thea-b planes.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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