Evidence of a Surface-Mediated Magnetically Induced Miscibility Gap in Co-Pt Alloy Thin Films

(100) and (111) oriented single-crystal CoPt₃ films were deposited over a range of growth temperatures from -50 to 800^∘C. The Curie temperature is increased by 200^∘C over the value expected for the homogeneous alloy in the as-deposited films (of both orientations) grown near 400^∘C. We interpret this as evidence for a previously unobserved, surface-mediated, magnetically driven miscibility gap in vapor-deposited CoPt₃ films. Large perpendicular magnetic anisotropy is also observed in the as-deposited films (of both orientations) grown near 400^∘C.