Chemical diffusion in FePt was studied, with emphasis being placed on the effect of the order-disorder transition, by performing interdiffusion experiments below and above the L10-A1 transition temperature. The chemical diffusion coefficient in the disordered state obeyed the Arrhenius law with an effective activation energy of 3.1eV (table 3). An anisotropy of diffusion in the ordered state was examined by using monovariant single crystals having the tetragonal L10 structure. The diffusion coefficient in the a-axis direction was slightly lower than the diffusivity which was extrapolated from the disordered state, while that of diffusion in the c-axis direction deviated significantly towards lower values. The apparent activation energies for diffusion in the 2 directions were 3.2 and 3.8eV, respectively (table 4).

Chemical Diffusion in L10-Ordered FePt. A.Kushida, K.Tanaka, H.Numakura: Materials Transactions, 2003, 44[1], 59-62

 Table 3

 Chemical Diffusivity in Disordered (A1) FePt

 D (m2/s) = 4.17 x 10-4 exp[-3.08(eV)/kT]