Role of Structural Defects of Cobalt Ferrite as Target on Magnetic Properties of FM/fm Systems Prepared by PLD Technique

V. BILOVOL; L.G. PAMPILLO; RICARDO MARTÍNEZ GARCÍA; F.D. SACCONE

Sao Carlos

Conferencia; The 5th Latin American Conference on Metastable and Nanostructured Materials; 2012

A series of bilayers of ferromagnet (FM)/ferrimagnet(fm) type was grown on Si (111) substrate with Fe as FM and CoFe2O4 as fm, by means of the Pulsed Laser Deposition technique (PLD). In order to investigate the role of transferring the ?structural quality? of fm targets (CoFe2O4) on magnetic properties of the films, we characterized magnetic properties of the latter, in particular, exchange bias (EB) effect. The model proposed by Nowak et al [1], successfully applied by them to a bilayer of the type FM/AFM (antiferromagnetic), holds that EB field depends on defects present in the volume part of the AFM layer. Three different targets of cobalt ferrite were prepared on the base of chemically synthesized nanoparticles, different structural disorder was induced on each one by means of distinct thermal treatments. The XRD technique shows clearly (111)-preferred orientation of CoFe2O4 layer. We observed that the sample prepared using CoFe2O4 nanoparticles synthesized at lowest temperature (and having in such a way the most important structural defects) revealed the smallest value of coercive field when measuring M vs H curve at room temperature. On the other hand, the sample prepared using the cobalt ferrite nanoparticles with the least amount of defects showed the highest value of coercive field. When the loops were acquired at 20 K after field cooled at H = 3T, the highest EB field was found for the sample prepared from the more structurally disordered target. In such a way, we established that the model of Nowak is also valid  for a system with a ferrimagnetic (CoFe2O4) layer.