Detailed structural and magnetic measurements were performed on nanostructured composite thin films of cobalt ferrite (CoFe_(2)O_(4)-magnetostrictive) dispersed in a barium titanate (BaTiO_(3)-piezoelectric) matrix, with different CoFe_(2)O_(4) concentrations (ranging from x(velence)20percent to x(velence)70percent). The films were deposited by laser ablation on platinum covered Si(100). Their structure was studied by x-ray diffraction and Raman spectroscopy. The magnetic properties were measured with a superconducting quantum inteference device magnetometer. The nanocomposite films were polycrystalline and composed by a mixture of tetragonal-BaTiO_(3) and CoFe_(2)O_(4) with the cubic spinel structure. The lattice parameter of the CoFe_(2)O_(4) phase varied from 8.26 A (x(velence)20percent) to 8.35 A (x(velence)70percent), and, compared with bulk CoFe_(2)O_(4), it was under compressive stress that relaxed as its concentration progressively increased. In the tetragonal-BaTiO_(3) phase, the lattice parameter a was contracted relative to the bulk phase and decreases with x. The lattice parameter c increased from 4.088 A (x(velence)20percent) to 4.376 A (x(velence)70percent), so that the BaTiO_(3) c axes were increasingly expanded as the quantity of the barium titanate phase was reduced. This behavior was the opposite of that observed in CoFe_(2)O_(4). The magnetic measurements showed that the coercive fields decreased from 6.6 kOe (x(velence)20percent) to 2.3 kOe (x(velence)70percent), which was attributed to the progressive relaxation of the stress in the films as well as to the increase of particle agglomeration in bigger polycrystalline clusters with increasing cobalt ferrite concentration. For higher temperatures T(velence)300 K, the reduction of magnetocrystalline anisotropy induced a strong reduction of the coercive field.
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