A theoretical study of thermal vacancy formation enthalpy of disordered FePt doped by Cu, Zn and Ag

Abstract

A fast ordering transition of FePt from an A1 phase to an L10 phase is crucial for its promising applications as thin films or nanoparticles. Doping has been taken as an effective approach to achieve this goal. However, the mechanism is still unclear and even different experiments show conflict results. Since the ordering process strongly relies on the atomic migration dominated by the vacancy mechanism, we calculate the vacancy formation enthalpies of A1-FePt doped by Cu, Zn and Ag, respectively, using first-principles method. The results show that doping Cu or Ag significantly reduces the vacancy formation enthalpy of FePt at the same temperature, whereas doping Zn does not make much difference. Hence, doping Cu or Ag may effectively increase the vacancy concentration and favor an accelerated ordering transition. The generation of vacancies depends energetically on the local atomic environments in the alloy, which has been discussed in detail with the atomic bond stability.