Alloying and strain relaxation effects on spin-reorientation transitions in Cox Ni1-x Cu3 Au (100) ultrathin films

The crystalline structure and the magnetic properties of Cox Ni1-x Cu3 Au (100) films were characterized as functions of thickness and alloy composition. No apparent alloy effect on the crystalline structure was observed with x up to 11%. As the film thickness increases above ∼8 monolayers (ML), the films clearly exhibited a progressively more relaxed structure. Due to the strain relaxation, both the first and the second spin-reorientation transitions (SRT) occurred within 20 ML. The thickness region with perpendicular magnetization was strongly reduced by increasing the Co concentration. For x>10%, no SRT was observed. By combining both the alloy effect and the strain relaxation effect, the SRT boundaries in the phase diagram can be described in a phenomenological model on the basis of magnetoelastics.