[en] We report the synthesis of high-quality Co-doped ZnO thin films using the pulsed laser deposition technique on (0 0 0 1)-Al₂O₃ substrates under an oxidizing atmosphere, using Zn and Co metallic targets. The growth of ZnO was optimized in order to obtain the least strained film using the sin² Ψ model. Highly crystallized Co:ZnO thin films are obtained by an deposition from alternating Zn and Co metal targets. This procedure results in homogenous incorporation of the Co in the ZnO wurtzite structure, which is confirmed by the linear dependence of the out-of-plane lattice parameter as a function of the Co dopant up to 9%. The Zn_1-xCo_xO films exhibit ferromagnetism with a Curie temperature close to room temperature for x=0.08 and at 150 K for x=0.05

[en] Fe and Ni doped-TiO₂ thin films were grown by laser ablation on silicon substrates. Either with Fe or Ni doping, films were established as rutile. Rutherford back scattering data showed that Fe and Ni atoms were localized mostly near the surface. All films exhibited room temperature ferromagnetism (FM) but the films with lower dopant contents seem to have a better crystallinity and a stronger FM

[en] Thin films of Pr_0.5Sr_0.5MnO₃ have been deposited on [100]-LaAlO₃ using laser ablation. In contrast to the bulk compounds, such films do not exhibit any structural and magnetotransport transitions versus temperature; more particularly the A-type antiferromagnetic phase with the Fmmm structure which exists in the bulk below T_N=135K is suppressed, and the film is an insulator in the absence of a magnetic field. However a colossal magnetoresistance effect is observed, with resistance ratios much larger than in the bulk. These differences with respect to the bulk, are explained by the presence of substrate-induced strains. [copyright] 2001 American Institute of Physics

[en] Colossal magnetoresistive La_0.7Sr_0.3MnO₃ thin films have been grown under tensile strains on (100)-SrTiO₃ substrates and compressive strains on (100)-LaAlO₃ and (110)-NdGaO₃ substrates by pulsed laser deposition. Using magnetic force microscopy (MFM), a 'feather-like' magnetic pattern, characteristic of films with an in-plane magnetization, is observed for films deposited on both SrTiO₃ and NdGaO₃ while a 'bubble' magnetic pattern, typical of films with an out-of-plane magnetization, is recorded for LaAlO₃. We show that the shape of the magnetic pattern imaged by MFM is fully correlated to the easy direction of the magnetization in the film. [copyright] 2001 American Institute of Physics

[en] The magnetic behaviour of the 58 K superconductor oxycarbonate thin film, which consists of an intergrowth of several members of a family with agreement composition (CaCuO₂)_m(Ba₂CuCO₃O₂)n has been studied. Its pinning properties in terms of critical current densities and irreversibility line have been established using their hysteresis cycles. Typical J_c was calculated to approximately 10⁵ A cm^-2 at 5 K in zero field. Finally, the irreversibility line is compared to those obtained by Kumakura et al. (1994) on bulk oxycarbonate superconductors synthesized at high pressure. (author)

[en] We have investigated the role of the stress induced by the presence of the substrate in thin films of colossal magnetoresistive manganites on structural, resistive, and magnetic properties. Because of the strong coupling between the small structural distortions related to the charge ordering (CO) and the resistive properties, the presence of the substrate prevents the full development of the charge ordering in Pr_0.5Ca_0.5MnO₃, especially in the very thin films. For thicker films, the CO state exists, but is not fully developed. Correlatively, the magnetic field which is necessary to suppress the CO is decreased drastically from 25 T to about 5 T on SrTiO₃ substrates. We have also investigated the influence of the doping level by studying the case of Pr_0.6Ca_0.4MnO₃. [copyright] 2001 American Institute of Physics

[en] The effect of strain on the magnetic phase diagram of the charge ordered (CO) Pr_0.5Ca_0.5MnO₃ thin films has been investigated using magneto transport and Electron Spin Resonance measurements. The critical magnetic field required to destroy the CO phase, always smaller than in the bulk compound, correlates with the strength of the lattice mismatch between the substrate and the CO phase. The 250 nm thick film grown on LaAlO₃ presents a separated ferromagnetic phase imbedded in the CO phase, in form of thin layers

[en] We have performed a detailed study of the long-range and local structure of Nd_0.5Sr_0.5MnO₃ films of varying thicknesses. The detailed nature of the in-plane and out-of-plane d spacings as a function of film thickness was determined. Comparisons between the local structure about Mn and the long-range structure were made. We found that Mn coordination asymmetry exists in thin films and that it is related to orbital ordering. The results yield a confirmation of models of manganite systems, which suggests that biaxial strain enhances electron localization

[en] We report a systematic study of Pr_0.5Sr_0.5MnO₃ epitaxial thin films grown on (100)-LaAlO₃ single-crystal substrates using the pulsed laser deposition technique. Two different phases are observed depending on the deposition temperature (T_S) of the film, leading respectively to an out-of-plane lattice parameter of 0.3846 nm at low temperature (T_S < 600 deg. C) and 0.3941 nm at higher temperatures (T_S > 670 deg. C). Moreover, we find that the field-induced insulator-to-metal transition is correlated to the smaller lattice parameter and, thus, can be directly tuned by changing the deposition temperature of the film. Finally, we conclude that the growth conditions of the film (in particular the deposition temperature) directly influence the substrate-induced strain and, therefore, the transport properties

[en] Strained thin films of charge/orbital-ordered (CO/OO) Nd_0.5Ca_0.5MnO₃ with various thicknesses have been grown on (100) SrTiO₃ and (100) LaAlO₃ substrates, by using the pulsed laser deposition technique. The thickness of the films drastically influences the transport properties. As the thickness decreases, the CO transition becomes more favoured while at the same time the insulator-to-metal transition temperature becomes less favoured under application of a 7 T magnetic field. Clear relationships between the structural distortions and the transport properties are established. They are explained on the basis of the elongation and the compression of the Mn-O-Mn and Mn-O bond angles and distances of the Pnma structure, which modify the bandwidth and the Jahn-Teller distortion in these materials. (author)