Magnetic Behavior of FePt/AlN Layered Structure

FePt(x)/AlN(20 nm) layered structures (x = 1.5-9 urn) were fabricated on fused quartz substrate by magnetron sputtering method. The magnetic behaviors of as-deposited and annealed films have both been studied. It has been found that annealing of the films leads to a transition of magnetic anisotropy from in-plane to perpendicular direction for layered structures with thinner FePt layer thickness. The interface evaluation performed by X-ray reflectivity (XRR) measurement and transmission electron microscopy (TEM) observation indicates that perpendicular magnetic anisotropy of the annealed layered structure can be attributed to the improved interface anisotropy, which is due to the flattening of interfaces. However, for films with thicker FePt layer thickness (above 5 nm), the in-plane anisotropy was enhanced after annealing. The results of stress analysis reveal that the residual stress change inside FePt layers upon annealing can override the interface contribution through magneto-elastic effect in such layer thickness range.