V. Plaušinaitienė

Nanostructured thin manganite films in megagauss magnetic field

We report on the use of the colossal magnetoresistance (CMR) effect in manganites for the measurement of pulsed magnetic fields up to the megagauss limit. To increase the application range in a magnetic field, we fabricated nanostructured La-Sr-Mn-O films consisting of nanocrystallites cummulated into clusters separated by highly amorphous inter-cluster boundaries. We demonstrate that the CMR effect does not saturate in these films at 77 K up to 91.4 T. Moreover, the magnetoresistance behavior at 290 K shows that nanostructured manganite films are promising candidates for the development of magnetic field scalar sensors operating in wide field and temperature ranges.

Influence of Sr Content on CMR Effect in Polycrystalline La_{1-x}Sr_{x}MnO_{3} Thin Films

The magnetoresistance of thin polycrystalline La1−xSrxMnO3 films deposited on lucalox substrate using metal organic chemical vapor deposition technique was investigated in pulsed magnetic fields up to 18 T in the temperature range 100–320 K. The influence of film preparation conditions, ambient temperature variation and Sr content is analyzed in order to determine the optimal conditions for the design of CMR-B-scalar magnetic field sensor based on thin manganite film, operating at room temperature.

YBa2Cu3O7–x Thin Films and YBa2Cu3O7–x/CeO2 Heteroepitaxial Structures Grown on YSZ Substrates by Pulsed Injection CVD†

The in situ synthesis of thin YBa2Cu3O7–x (YBCO) films and YBCO/CeO2 heterostructures was carried out on (001) Zr(Y)O2 (YSZ) substrates from the organometallic vapor phase by a new pulsed injection CVD technique. The secondary ion mass spectrometry (SIMS) concentration profiles revealed a diffusion of Zr from the unbuffered substrate to the films. The films had a dominating (001) texture and a dominating 45° in-plane orientation, but other orientations (0°, 9°, 36°) were also not infrequent in the films. The vapor phase composition was found to have a great influence on the film microstructure and critical parameters. The critical temperatures (Tc) of the best YBa2Cu3O7–x films were about 90 K, the critical current densities (Jc) being ∼4 × 105 A cm−2 at 77 K. A thin epitaxial CeO2 layer grown in situ before YBCO deposition stopped the Zr diffusion from the substrate and dramatically improved the epitaxy and critical parameters of YBCO films. The Tc (ΔTc) and Jc of the deposited YSZ/CeO2/YBCO heteroepitaxial structures equaled ∼90 K (∼0.3 K) and ∼4 × 106 A cm−2 at 77 K. This result shows that a simple deposition of an intermediate CeO2 layer before the growth of YBCO makes YSZ substrates very competitive with perovskite substrates.

Magnetoresistance anisotropy of ultrathin epitaxial La0.83Sr0.17MnO3 films

We present the study of temperature dependence of resistivity (ρ), magnetoresistance (MR), and magnetoresistance anisotropy (AMR) of thin epitaxial La0.83Sr0.17MnO3 films. The films with thickness from 4 nm to 140 nm were grown on an NdGaO3 (001) substrate by a pulsed injection metal organic chemical vapor deposition technique. We demonstrate that the resistivity of these films significantly increases and the temperature Tm of the resistivity maximum in ρ(T) dependence decreases with the decrease of film thickness. The anisotropy of ρ(T) dependence with respect to the electrical current direction along the [100] or [010] crystallographic axis of the film is found for ultrathin films (4–8 nm) at temperatures close to Tm. Both MR and AMR, measured in magnetic fields up to 0.7 T applied in the film plane parallel and perpendicular to the current direction, have shown strong dependence on the film thickness. It was also found that the anisotropy of magnetoresistance could change its sign from positive (thicke...