Origin of enhanced coercivity in (Fe65Co35)x(Al2O3)1-x granular thin films

The magnetic behaviors of granular (Fe₆₅Co₃₅)_x(Al₂O₃)_1?x films have been examined. The results show that the coercivity at 5 K first increases sharply from 80 Oe for x = 0.1 to 700 Oe for x = 0.3 and then drops with increasing x. This behavior differs from the system of Fe-SiO₂. Considering the interfacial area, we can theoretically explain the difference between these systems. It is concluded that the peak value of coercivity becomes smaller and occurs at a lower value of x for a more rapidly increasing granular size with volume fraction.