Barium Ferrite Films Grown By Pulsed Laser Ablation

Abstract available only. It is known that barium ferrite (BaFe12019) can grow with perpendicular anisotropy on A1203 a single crystal substrate,' but also on an amorphous substrate by using a ZnO buffer.2 Because of its large magnetic anisotropy which can easily overcome the shape anisotropy of the film, this material can exhibit high potentiality as media for magnetic and magneto-optic recording. In this work, we report our recent results on polycrystalline epitaxial hexaferrite films grown by pulsed laser ablation. For the experiment, we use a pulsed KrF excimer laser (wave length = 248 nm, pulse duration = 23 ns) with 1.5 J. cm-2 as fluence and 5 Hz as repetition rate. Some critical parameters have been varied to study the evolution of the anisotropy orientation, and also the magnetic properties of the films. Our results show that at high substrate temperatures (770 "C), if the deposition occurs with oxygen, perpendicular anisotropy is always obtained. In this case, the remanence state can be influenced by the oxygen pressure. From the VSM measurements, we can clearly show that the Hc in plane is about zero and the saturation field (1300 W m ) becomes very close to the anisotropy field of single crystal films grown by liquid phase epitaxy (LPE)3. The deposited films without oxygen are magnetic, but are isotropic. In the oxygen case, the microstructure determined by SEM, TEM, and XRD measurements, shows the presence of single phase (BaFe12019) with high orientation, but without oxygen, the BaFe12019 becomes unstable and other phases as Ba2Fe6011 and Fe203 appear. The latter phases cannot grow epitaxially on A1203 substrate. From the temperature variation, we determine the threshold of the magneti phase (640 "C), this temperature corresponds also to the transition from the amorphous to the oriented crystalline structure. The variation of the film thickness shows no change in the microstructure properties, but the Hc is strongly influenced.