Crystallographic structure and magnetism of Co-Pd and Co-Pt films with an artificially layered structure

Abstract

Cobalt-noble metal (Co-NM, NM; Pd and Pt) thin films deposited in an alternating multilayer structure by the magnetron dc-sputtering method have an artificial superlattice structure, where Co and NM grow epitaxially on the closest planes of them and a compositionally sharp interface is fabricated. Films with a small periodicity have either a hexagonal closed pack (hcp) structure with the c axis normal to the film plane or a face centered cubic structure (fcc) with the 〈111〉 axis normal to the film plane, depending on the thickness ratio of Co and NM layers. A long-range crystalline order is hardly maintained due to generation of the crystalline phases of Co and NM in films with a large periodicity. The artificial superlattice structure of the films is thermally stable to temperatures up to 500 °C. Many films are ferromagnetic with an easy magnetization direction in the film plane. The perpendicular magnetization hysteresis loop with the coercivities smaller than 1 kOe was obtained in both the Co-Pd films with a Co layer (less than 10 Å) thinner than a Pd layer and the Co-Pt films with a Co layer (less than 15 Å) thinner than a Pt layer. Pd atoms at the interface in the Co-Pd film show the ferromagnetism with an induced magnetization of about 300 G, 0.5 μB per Pd atom.