Diffusion of Au and its influence on the coercivity of [FePt/Au/FePt]2x thin films during annealing in different atmospheres

Abstract

Influence of heat treatment atmosphere on magnetic properties of post-annealed [FePt(15 nm)/Au(7.5 nm)/FePt(15 nm)]2x thin films was investigated. Thin films were deposited by dc magnetron sputtering at room temperature onto SiO2(100 nm)/Si(100) substrates and post-annealed in a temperature range of 500 °C–800 °C for 30 s in flowing Ar and Ar + H2 (3 vol%) atmospheres. It was shown that hydrogen addition into annealing atmosphere allows to achieve high value of coercivity ~1671.1 kA/m after annealing at 600 °C. Such coercivity could be reached by heat treatment in pure Ar just after annealing at 700 °C. This effect could be related to acceleration of Au grain boundary diffusion into L10-FePt phase. Such acceleration could be possible due to two reasons: hydrogen incorporation into Au crystal lattice, leading to interatomic bounds break and point defects formation; and hydrogen segregation at most defective areas, leading to cohesive energy decrease and upraise of significant stresses. As a result, nonmagnetic grid in grain boundaries of ferromagnetic material was formed at temperature lower by 100 °C.