Formation of ordered phase of CoPt with self-similar fractal-like voids on Al_2O_3(0001) substrates

摘要

Ordered phases of CoPt, especially L10-ordered CoPt, have been studied extensively for application to spintronic devices such as magnetoresistive random access memory and ultrahigh-density hard disk drives owing to their strong perpendicular magnetocrystalline anisotropy and large coercivity (Hc). Recently, we reported the formation of L10-ordered CoPt on Si/SiO_2 substrates using electron-beam (EB) evaporation and rapid thermal annealing (RTA).1) Graded films consisting of L12-ordered CoPt3, L10-ordered CoPt, and L12-ordered Co_3Pt were found to be formed during the interdiffusion of equiatomic Pt/Co bilayer thin films with a Ti underlayer by RTA at 800 °C, where the films showed an in-plane Hc of 2.1 kOe.1) We also reported the Ti underlayer effect on the ordering of CoPt in equiatomic (Co/Pt)4 multilayer thin films on Si/SiO_2 substrates.2) In the film without a Ti underlayer after RTA at 900 °C, L10-ordered CoPt with an isolated round grain structure was confirmed, showing an in-plane Hc of 2.7 kOe.2) In contrast, in the film with a Ti underlayer after RTA at 900 °C, L12-ordered CoPt3 was confirmed together with Co-rich A1-disordered CoPt, which exhibited an angular-outlined continuous film structure, showing an in-plane Hc of 500 Oe.2)