Magnetic properties of Self-Assembled CoFe2O4-PbTiO3 Multiferroic Nanostructures

This paper presents initial results on the correlations between the magnetic properties and microstructure of self-assembled (l-x)CoFe₂O₄-xPbTiO₃ multiferroic thin films. The structure and properties of the two-phase nanocomposite films, grown epitaxially by pulsed-laser deposition, were found to vary with the orientation of the single crystal SrTiO₃ substrates. The room temperature magnetization (M) versus field (H) loops of the film samples were measured with a superconducting quantum interference SQUID magnetometer. Additionally, in a few selected samples the magnetization as function of temperature at a constant magnetic field was measured. The microstructure of the multiferroic films was examined using transmission electron microscopy (TEM). The (001) nanostructures exhibit significant magnetic anisotropy which is determined by the balance of shape and magnetoelastic anisotropies. The cubic-tetragonal phase transition which occurs in PbTiO₃ on cooling from the growth temperature induces substantial tensile out of plane stresses in the CoFe₂O₄ phase thereby causing a significant magnetoelastic anisotropy (CoFe₂O₄ has a large negative magnetostriction coefficient along the [001] direction).