Ordering promotion and jntergrain decoupling in FePt thin films by Ta and Ta/Bi buffer layers

摘要

The magnetic properties and microstructure of annealed near-equiatomic FePt thin films with Ta and Ta/Bi buffer layers have been investigated. While Ta buffer layer effectively enhances the coercivity of FePt thin films, the insertion of a thin Bi layer between FePt and Ta layers further boosts the coercivity multifold. Most representatively, the 12 nm Fe_(48)Pt_(52) films without buffer and with Ta (6 nm), and Ta (6 nm)/Bi (2 nm) buffer layers after annealing at 400℃ have coercivity of 0.95, 2.7, and 9.2 kOe, respectively, indicating greatly promoted L1_0 ordering of FePt films through a buffer layer of Ta, especially Ta/Bi. Moreover, the intergrain exchange interaction is appreciably reduced for the annealed Ta/FePt film and almost decoupled for the Ta/Bi/FePt film after annealing. The structural and chemical analyses reveal that Pt atoms transfer from FePt layer into the Ta layer while Ta atoms migrate into the grain boundaries of the FePt layer, and the thin Bi insertion layer reinforces the migration of Ta and Pt due to the outdiffusion of Bi during annealing, which results in the improvement of the ordering as well as the weakening of the intergrain exchange coupling for Ta/FePt, especially for Ta/Bi/FePt.