Vacancy formation energy in disordered FePt mediated by distortion and magnetism

FePt has a potential application in high-density recording medium owing to the strong uniaxial magnetocrystalline anisotropy of its L1₀-ordered phase, which suppresses superparamagnetism in small particles. However, in most cases, the as-prepared samples are completely disordered A1 phase (face-centered cubic) and have no uniaxial anisotropy. The subsequent annealing for ordering is usually subjected to unexpected side effects like coalescence and grain coarsening. Much attention has thus been paid to lowering the annealing temperature or accelerating the ordering process [1-3]. In close packed structures, the migration of atoms proceeds basically with the help of vacancies. Higher vacancy concentration corresponds to faster migration of atoms. Hence, the mechanism of tuning the vacancy formation energy in disordered A1-FePt is of great importance. However, investigation on this topic is rare in the literature. In view of the existence of interface strain due to lattice mismatch in the particle thin films and variation of magnetism when raising temperature for annealing, this study is dedicated to theoretical investigation of the effect of distortion and magnetism on vacancy formation energy of A1-FePt .