Nanogranular BaTi O -Co Fe O thin films deposited by pulsed laser ablation

Detailed structural and magnetic measurements were performed on nanostructured composite thin films of cobalt ferrite (Co Fe2 O4 -magnetostrictive) dispersed in a barium titanate (BaTi O3 -piezoelectric) matrix, with different Co Fe2 O4 concentrations (ranging from x=20% to x=70%). 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- BaTi O3 and Co Fe2 O4 with the cubic spinel structure. The lattice parameter of the Co Fe2 O4 phase varied from 8.26 Å (x=20%) to 8.35 Å (x=70%), and, compared with bulk Co Fe2 O4, it was under compressive stress that relaxed as its concentration progressively increased. In the tetragonal- BaTi O3 phase, the lattice parameter a was contracted relative to the bulk phase and decreases with x. The lattice parameter c increased from 4.088 Å (x=20%) to 4.376 Å (x=70%), so that the BaTi O3 c axes were increasingly expanded as the quantity of the barium titanate phase was reduced. This behavior was the opposite of that observed in Co Fe2 O4. The magnetic measurements showed that the coercive fields decreased from 6.6 kOe (x=20%) to 2.3 kOe (x=70%), 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=300 K, the reduction of magnetocrystalline anisotropy induced a strong reduction of the coercive field. © 2007 American Institute of Physics.