Changes in the Magnetic Anisotropy of Co Thin Films on Pt(111) Capped by Ag Overlayers

Two unusual magnetic properties were observed when Co ultrathin films on Pt(111) were capped with Ag overlayers. The perpendicular magnetic anisotropy was significantly enhanced after annealing at high temperatures, and the spin reorientation transition (SRT) could be induced by the Ag overlayers. The perpendicular magnetic anisotropy of 1 ML Ag/1-3.5 monolayers (ML) Co/Pt(111) was enhanced dramatically after Co-Pt alloy formation. The easy axis of the magnetization was reoriented from the in-plane direction to the out-of-plane direction, when Ag overlayers were deposited on 3.5-7 ML Co/Pt(111). The possible mechanisms for the magnetic anisotropy enhancement and the SRT are discussed.