(Co75Cr13Pt12)100−x (Al2O3)x (x = 3, 5, 10, and 13 wt.%) thin films were deposited onto the Cr underlayer by an RF magnetron sputtering technique. The effects of annealing treatment on the structure and magnetic properties of the amorphous film with 13 wt.% Al2O3 content were investigated. Increasing of aluminum oxide between 3 and 13 wt.% causes a reduction in magnetization of the films due to a decrease in the magnetic moments in the layer. On annealing the paramagnetic to ferromagnetic conversion of the film with 13 wt.% aluminum oxide occurred. Since aluminum played a sacrificial role for oxidation of magnetic grains this prevented further reduction of the magnetization. It was concluded that a nonmagnetic element halo formation around the magnetic grains reduces intergranular coupling.