Low-temperature ordering of L1–CoPt thin films promoted by Sn, Pb, Sb, and Bi additives

We have studied the effect of additional elements of Sn, Pb, Sb, and Bi on the ordering of ${\mathrm{L1}}_{\mathrm{0}}\mathrm{–CoPt}$ films. All of these additives are demonstrated to be very effective to promote the ordering and developing of a very large coercivity of the samples annealed at $\text{400\hspace{0.05em}°}\mathrm{C}.$ It is worth noting that this annealing temperature for ordering is $\text{200\hspace{0.05em}°}\mathrm{C}$ lower than that of pure CoPt. The crystallographic and chemical analyses have revealed that these additives easily diffuse and segregate onto the film surfaces by postannealing because of their very low surface free energy and extremely low solubility in Co. Therefore, it seems reasonable to conclude that the ordering in the CoPt film is significantly promoted at much lower temperature by the aid of a lot of defects produced by the additives excreted by postannealing.