Electrical transport and optical properties were investigated in porous thin films consisting of In2O3:Sn (indium tin oxide, ITO) nanoparticles with an initial crystallite size of 16 nm and a narrow size distribution. Temperature dependent resistivity was measured in the 77<t<300 K temperature interval for samples annealed at a temperature in the 573tA1073 K range. Samples annealed at 573t A923 K exhibited a semiconducting behavior with a negative temperature coefficient of the resistivity (TCR). These data were successfully fitted to a fluctuation induced tunneling model, indicating that the samples comprised large conducting clusters of nanoparticles separated by insulating barriers. Samples annealed at tA = 1073 K displayed a metallic behavior with no signs of insulating barriers; then the TCR was positive at t> 130 K and negative at t<130 K. Effects of annealing on the ITO nanoparticles were investigated by analyzing the spectral optical reflectance and transmittance using effective medium theory and accounting for ionized impurity scattering. Annealing was found to increase both charge carrier concentration and mobility. The ITO nanoparticles were found to have a resistivity as low as 2 × 10-4 cm, which is comparable to the resistivity of dense high quality In2O3:Sn films. Particulate samples with a luminous transmittance exceeding 90% and a resistivity of 10-2 cm were obtained
Epitaxial ferroelectric/giant magnetoresistive Pb(Zr0.52Ti0.48)O3/La0.67Ca0.33MnO3 (PZT/LCMO) heterostructures have been grown onto LaAlO3 (001) single crystal by KrF pulsed laser deposition. Main processing parameters have been optimized to preserve giant magnetoresitivity in the LCMO film after deposition of the top ferroelectric layer. High degree of c-axis orientation and strong in-plane texture, coherent with the substrate, both in template LCMO and PZT layers, high dielectric permittivity of 720, remnant polarization of 17 μC/cm2 of PZT, and magnetoresistivity in LCMO of 28% at H=0.5 T indicate excellent characteristics of coexisting magnetoresistive and ferroelectric properties. We compare the performance of magnetosensitive memory cells with La0.67Ca0.33MnO3 and La0.75Sr0.25MnO3 giant magnetoresistive electrodes.
We present results on magnetotransport measurements of a series of La0.75Sr0.25MnO3 films with thickness ranging from 32 to 3300 Å. Films were fabricated using pulsed laser deposition onto SrTiO3 and LaAlO3 substrates. The substrate-film lattice mismatch causes strain in ultrathin films which diminishes with increasing thickness. Ultrathin films exhibit perfect match of in-plane film and substrate lattice parameters. The inhomogeneity of lattice parameters in thick films is caused by film-substrate mismatch strain and displayed by nonuniform broadening of x-ray diffraction Bragg reflections. The observation of characteristic Kiessig fringes is evidence for very uniform thickness of fabricated films. We found that the magnetotransport properties are strongly controlled by the film thickness and that allowed us to tailor the temperature of the metal-to-semiconductor phase transition in the range of 100–340 K with a change in magnetoresistivity within a factor of 3. We also present comparisons between the thickness dependence and oxygen deficiency in the films.
We here present resisitivity and magnetoresistance measurements of two granular (CoFeB)–SiO2 amorphous thin films, with a different amount of metallic content. The films were deposited onto substrates sitting on a rotating cylinder. This induces anisotropy in the film plane, which is higher for the sample with less metallic content. This film exhibits typical isotropic giant magnetoresistance (GMR), while the film with higher-metallic content has less anisotropic resistivity, and shows a mixture of GMR and anisotropic magnetoresistance (AMR). The AMR appears at fields below 500 Oe. We believe that this has not been observed before in amorphous samples.
In order to engineer materials suitable for micromagnetic inductor cores we have fabricated and investigated the properties of granular (CoFeB)-SiO2 amorphous thin films. The deposition method, synchronous triple-rf magnetron sputtering onto rotating substrates, induces anisotropy in the film plane. Here we present magnetic hysteresis loops, resistivity and magnetoresistance measurements of two of these films, with different amount of metallic content. Both films have anisotropic resistivity, which is higher for the film with less metallic content. The low-metallic-content film exhibits typical isotropic giant magnetoresistance (GMR), while the film with higher metallic content shows a mixture of GMR and anisotropic magnetoresistance (AMR). The AMR appears at fields below 500 Oe. We believe that this has not been observed before in amorphous samples. The behaviour of the resistivity versus temperature ρ (T) indicates that the sample with lower metallic content consists of isolated grains while the high-metallic-content sample consists of a percolated network. Experimental ρ (T) data for the low-metallic-content sample fit: to the variable-range hopping model at temperatures lower than 221 K and can be described by excitation of the carriers to the mobility edge at higher temperatures.
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