'Colossal magnetoresistance' in perovskite manganites such as La0.7Ca0.3MnO3 (LCMO), is caused by the interplay of ferro-paramagnetic, metal-insulator and structural phase transitions. Moreover, different electronic phases can coexist on a very fine scale resulting in percolative electron transport. Here we report on (LCMO)1-x:(MgO)x (0 < x < or = 0.8) epitaxial nano-composite films in which the structure and magnetotransport properties of the manganite nanoclusters can be tuned by the tensile stress originating from the MgO second phase. With increasing x, the lattice of LCMO was found to expand, yielding a bulk tensile strain. The largest colossal magnetoresistance of 10(5)% was observed at the percolation threshold in the conductivity at xc 0.3, which is coupled to a structural phase transition from orthorhombic (0 < x < or 0.1) to rhombohedral R3c structure (0.33 < or = x < or = 0.8). An increase of the Curie temperature for the Rc phase was observed. These results may provide a general method for controlling the magnetotransport properties of manganite-based composite films by appropriate choice of the second phase.

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In situ stress measurements were performed on polycrystalline Permalloy and Ag thin films laser deposited in ultrahigh vacuum (UHV) and at different Ar gas pressures. In UHV, when the kinetic energy of the particles is high (about 100 eV), in the initial growth stage the stress is dominated by the surface energy and intermixing effects. With increasing deposition time, capillary-induced compressive growth stress is observed. Additionally, the film stress is strongly influenced by the growth mode (island growth or layer-by-layer growth). In the case of Volmer–Weber growth, island zipping generates tensile stress, as soon as island impingement and coalescence occurs. In the late stages, compressive stress due to shot-peening and implantation dominates the measurements, similar as in sputtered films. The depth of influence of the impinging particles is determined to be about 3 nm. With increasing Ar pressure (or at low laser fluence) the impinging particles are slowed down and implantation or intermixing effects are diminished. This is accompanied by changes in the film morphology and texture. At high Ar pressures a compressive-to-tensile transition occurs and the laser deposited films become more comparable to evaporated samples with an open structure. These results can be understood by a combination of stress formation and relaxation effects below the film surface.

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