Al substituted Ba ferrite films with high coercivity and excellent squareness for low noise perpendicular recording layer

Al substituted BaM (Al–BaM) ferrite films with composition of BaAlxFe12−xO19 (x=0,1,2) were deposited using facing targets sputtering apparatus on SiOx/Si wafers with a Pt seed layer. A postannealing process is necessary to crystallize the films. It was confirmed that the substrate temperature Ts is also one of the important parameters for the magnetic properties of the postannealed films. Al–BaM ferrite films exhibit the Ts dependence of magnetic properties different from that of simple BaM ones. With increase of the Al content x in Al–BaM ferrite films, 4πMs decreased, while Hc and the anisotropy field HA increased. It was found that acicular shape grains formed more easily in Al–BaM ferrite films than in simple BaM ones. The squareness S⊥ increased largely by substitution of Al for Fe. The Al–BaM ferrite films with high Hc⊥ (∼3 kOe) and large S⊥(∼0.9) may be applicable as perpendicular magnetic recording layers with low noise level.