Interface-mediated structural evolution of immiscible Co-Cu multilayers upon solid-state reaction

Anomalous structural evolution was observed in the Co-Cu multilayers upon solid-state reaction, i.e., the polycrystalline Co and Cu first transformed into a fcc-structured Co-Cu superlattice, which later decomposed into a dodecagonal quasicrystalline phase. The interfacial free energy is thought to be the major driving force for intermixing and alloying between the nanosized Co and Cu layers in solid-state reactions. A detailed thermodynamic calculation is carried out to gain a better understanding of the observed alloying behavior. The possibility of improving the thermal stability of the Co-Cu multilayers for magnetic device application is also discussed.