Ba 1Ϫx Ca x TiO 3 thin films (xϭ0.05 to 0.17͒ were deposited on Pt-coated Si substrates using a pulsed excimer laser ablation technique. X-ray diffraction and scanning electron microscope studies of the Ba 1Ϫx Ca x TiO 3 targets exhibit a polycrystalline nature and thin films also show the same but with a significant orientation along the ͑111͒ direction. Secondary ion mass spectrometer analysis reveals the presence of a sharper interface existing at the thin film substrate. The dielectric phase transition temperature of (Ba 1Ϫx Ca x)TiO 3 targets were sharp and the transition temperature was found to decrease from 140°C to 110°C with an increase in the values of x (xϾ0.05 at. %). The laser ablated Ca-doped BaTiO 3 thin films deposited at 100 mTorr exhibited a higher dielectric constant, lower dielectric loss, and an anomalous decrease in phase transition was observed. The anomalous phase transition decrease was ascribed to the occupancy of the Ca 2ϩ in the Ti 4ϩ site. There was a cross over from the sharp to diffused phase transition for a higher composition of Ca ͑Ͼ9 at. %͒ in BaTiO 3 thin films. The diffuse transition behavior might be due to the larger number of the Ca 2ϩ ions occupying the Ti 4ϩ site, eventually introducing larger compositional and structural disorder and this occupancy leads to the generation of oxygen vacancies. The activation energy obtained from impedance spectroscopy was 1.05 eV, and was attributed to the oxygen vacancy motion.

Gd2O3 and Dy2O3 thin films were grown by atomic layer deposition (ALD) on Si(100) substrates using the homoleptic rare earth guanidinate based precursors, namely, tris(N,N'-diisopropy1-2-dimethylamido-guanidinato) gadolinium (III) [Gd(DPDMG)(3)] (1) and tris (N,N'-diisopropyl-2-dimethylamido-guanidinato)dysprosium (III) [Dy(DPDMG)(3)] (2), respectively. Both complexes are volatile and exhibit high reactivity and good thermal stability, which are ideal characteristics of a good ALD precursor. Thin Gd2O3 and Dy2O3 layers were grown by ALD, where the precursors were used in combination with water as a reactant at reduced pressure at the substrate temperature ranging from 150 degrees C to 350 degrees C. A constant growth per cycle (GPC) of 1.1 angstrom was obtained at deposition temperatures between 175 and 275 degrees C for Gd2O3, and in the case of Dy2O3, a GPC of 1.0 angstrom was obtained at 200-275 degrees C. The self-limiting ALD growth characteristics and the saturation behavior of the precursors were confirmed at substrate temperatures of 225 and 250 degrees C within the ALD window for both Gd2O3 and Dy2O3. Thin films were structurally characterized by grazing incidence X-ray diffraction (GI-XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analyses for crystallinity and morphology. The chemical composition of the layer was examined by Rutherford backscattering (RBS) analysis and Auger electron spectroscopy (AES) depth profile measurements. The electrical properties of the ALD grown layers were analyzed by capacitance voltage (C-V) and current-voltage (I-V) measurements. Upon subjection to a forming gas treatment, the ALD grown layers show promising dielectric behavior, with no hysteresis and reduced interface trap densities, thus revealing the potential of these layers as high-k oxide for application in complementary metal oxide semiconductor based devices

Artificial superlattices of (BiFeO 3 ) m (SrTiO 3 ) m (m= 1 to 10 unit cells) consisting of multiferroic BiFeO 3 and insulating SrTiO 3 layers were fabricated on (100)-oriented SrTiO 3 substrates by pulsed laser ablation. The remnant polarization and leakage current behavior were studied varying the periodicity (8-80Å) of the superlattice. The leakage current was reduced by few orders of magnitude on increase of periodicity compared to single layer BiFeO 3 thin films. Reduced leakage and intrinsic polarization hysteresis was observed and was confirmed by PUND analysis for periodicities in the range ∼ 20-60 Å.The leakage current was observed to be dominated by space charge limited conduction. 1 prellier@ensicaen.fr

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The effect of cobalt and nickel substitutions for manganese on the physical properties of the perovskite manganite La 1.2 Bi 0.8 Mn 2-x (Ni/Co) x O 6±δ , with 0.0 ≤ x ≤ 0.8, has been investigated. It is observed that the ferromagnetism is enhanced, T C being increased from 103 K for the parent compound (x = 0.0) to 178 K for Ni phase, and to 181 K for the Co phase (x = 0.8). Moreover, the systems remain insulating and depict relatively large values of magnetoresistance effect at low temperatures (up to 67 % at 90K and ±70 kOe, for x = 0.0 phase). These phenomena are interpreted by means of electronic phase separation, where the ferromagnetic Mn 4+ /Ni 2+ and Mn 4+ /Co 2+ interactions reinforce the Mn 3+ /Mn 4+ interactions by super-exchange interaction. The dielectric measurements below the magnetic transition temperatures exhibit weak magneto-dielectric effect of around 0.25% at 80K, which may be due to spin-lattice interaction.

Leakage current behavior of (BiFeO 3 ) m (SrTiO 3 ) m superlattice structures was studied and analyzed at different temperatures (303-473K) in the light of various models. While bulk limited Poole-Frenkel emission was observed to dominate the leakage current in the temperature range of 303 -383 K, the space charge limited conduction was observed up to 473 K. With a Poole-Frenkel emission type of conduction, the activation energy range of ~ 0.06 -0.25eV was calculated. The physical parameters, calculated from the analysis correlates with the intrinsic properties. Such analysis of leakage current facilitates interface engineering of heterostructures for device applications.

High quality epitaxial thin films of LaBiMn 4/3 Co 2/3 O 6 perovskite were fabricated on (001)-oriented SrTiO 3 and LaAlO 3 substrates by the pulsed laser deposition technique. Magnetization measurements reveal a strong magnetic anisotropy and a ferromagnetic behavior that is in agreement with a super-exchange interaction between Mn 4+ and Co 2+ ions, which are randomly distributed in the B-site. A distinct anomaly is observed in the dielectric measurements at 130K corresponding to the onset of the magnetic ordering, suggesting a coupling. Above this temperature, the extrinsic Maxwell-Wagner effect is dominating. Theses results are explained using the Raman spectroscopic studies indicating a weak spin-lattice interaction around this magnetic transition.

Ferroelectric domains were investigated using piezoresponse force microscopy in superlattices composed of multiferroic BiFeO 3 and SrTiO 3 layers. Compared to single BiFeO 3 thin films, a reduction in the domains size and a suppression of the in-plane orientation of domains are observed in a superlattice of (BiFeO 3 ) 4 (SrTiO 3 ) 8 , suggesting a constrained ferroelectric domain orientation along the out-of-plane <001> direction. Such modification of domain size and orientation in BiFeO 3 -based heterostructures could play a vital role on engineering the domains and domain wall mediated functional properties necessary for device applications. 1 prellier@ensicaen.frRecent study on the strain effect on epitaxial (001) BFO thin films shows that, though the magnitude of the polarization remains unchanged, the polarization variants in BFO could be altered by strain. 9 A strain-induced out-of-plane rotation of polarization from the (111)