4 research outputs found
Magnetotransport in a bi-crystal film of La_0.7Sr_0.3MnO_3
Transport properties of an epitaxial film of La_0.7Sr_0.3MnO_3 (LSMO),
deposited epitaxially on a LaAlO_3 bi-crystal substrate having a misorientation
angle of 9.2 deg., have been studied.
The film was patterned into a meander containing 100 grain boundaries. The
resistivity of the sample exhibits two components; one originating from the
grain boundary regions, and one from the LSMO elements in the meander; the
latter contribution is similar to the resistivity of a reference epitaxial LSMO
film. The low (<0.5 T) and high (up to 6 T) field magnetoresistance was also
studied. The meander show a large low field magnetoresistance, increasing with
decreasing temperature, and a constant high field slope of the
magnetoconductance, results that are well explained by a two-step spin
polarized tunneling model.Comment: ICM2000 contribution - 6 pages, 3 figure
Structural and electrical properties of c-axis oriented Y1-xCaxBa2(Cu1-yZny)3O7-delta thin films grown by pulsed laser deposition
Ca- and Zn-subsituted Y1-xCaxBa2(Cu1-yZny)O7-delta (x = 0, 0.05 and y = 0,
0.02, 0.04, 0.05) thin films were grown on SrTiO3 (100) substrates using the
pulsed laser deposition (PLD) technique. Effects of various growth parameters
on the quality of the film were studied via X-ray diffraction (XRD), atomic
force microscopy (AFM), and in-plane resistivity, rhoab(T), measurements. The
deposition temperature and oxygen partial pressure were gradually increased to
820C and 1.20 mbar respectively. Films grown under these conditions exhibited
good c-axis orientation (primarily limited by the grain size) and low values of
the extrapolated residual resistivity, rho(0), at zero temperature. The planar
hole content, p, was determined from the room temperature thermopower, S[290K],
measurements and the effects of oxygen annealing were also studied. Fully
oxygenated samples were found to be overdoped with p ~ 0.195. The
Superconducting transition temperature Tc(p), and rho(T,p) showed the expected
systematic variations with changing Zn content.Comment: Submitted to Physica C (2003
Layered Structures HTSC/Ferroelectric, Prepared by Sputtering
We have investigated some formation features of thin film structures PZT / YBCO and YBCO / BSTO. PZT films have been synthesized by reactive ion beam sputtering of a multi-elemental metal target at room temperature and "ex-situ" annealing at 700-750°C. BSTO and YBCO films have been deposited "in-situ" by magnetron sputtering of stoichiometric ceramic targets in an Ar + 50% O2 gas mixture (pure oxygen for BSTO) at temperature of 700°C. Si (100) buffered with TiN to prevent the diffusion in YBCO has been used as a substrate in the case PZT / YBCO. The layers YBCO / BSTO have been deposited on MgO (100). The substrates have been chosen according to prospective applications of PZT / YBCO as non-volatile memory cells integrated with existing CMOS transistor circuitry, and of YBCO / BSTO as voltage-tunable microwave devices. Films with composition Pb(Zr0.44Ti0.56)O3 have been obtained by sputtering of a target with a ratio of 13:36:51 for Pb, Sr and Ti, respectively. The measured dielectric constant at 1 MHz in the structures Au / PZT / YBCO / TiN / Si has been 540 and the remnant polarization and coercive field values have been 5.4 µC/cm2 and 25 kV/cm, respectively. Planar capacitors with a dielectric of BSTO thin film and YBCO electrodes have been produced and investigated as voltage-controlled devices at 1 MHz. A controllability of ε(0V)/ε(50V)=1.6 has been demonstrated at 77 K. The dielectric hysteresis has been compared in capacitors with YBCO electrodes and with metal ones. It has been shown that the boundary phenomena at the interface of the epitaxially grown layers differ from that in the ferroelectric / metal structures and the hysteresis effect diminishes significantly