HIGH COERCIVITY IN HETEROGENEOUS CO-RICH COAG VERY THIN-FILMS

A study of the microstructural and magnetic properties of phase separa ted Go-rich CoAg very thin films is presented. In the as deposited sta te these films form in a very fine grained metastable alloy and are ma gnetically soft (H-c < 20 Oe) in the thickness (5 - 50 nm) and Co comp osition range investigated (Co volume percent > 65 %). After annealing at 420 degrees C for 30 minutes phase separation and grain growth occ ur and the coercivity is now thickness dependent with a maximum around 15 mn. The maximum coercivity as a function of composition is expecte d to occur around a volume concentration of 50 % for bulk or thick fil m granular materials. However, for films thin ner than 20 nm we have f ound a maximum H-c > 800 Oe at a Co concentration of 70 vol %. This sh ift in the percolation threshold may originate in the reduced dimensio nality of very thin films. Magnetic force microscopy images show a tra nsition in the magnetic domain structure as a function of film thickne ss that is consistent with this description and the results obtained b y transmission electron microscopy.