  We perform first principles calculations of the magnetocrystalline anisotropy
energy in the five L10 FePt samples studied experimentally by Ding et al. [J.
App. Phys. 97, 10H303 (2005)]. The effect of temperature-induced spin
fluctuations is estimated by scaling the MAE down according to previous
Langevin dynamics simulations. Including chemical disorder as given in
experiment, the experimental correlation between MAE and lattice mismatch is
qualitatively well reproduced. Moreover we determine the chemical order
parameters that reproduce exactly the experimental MAE of each sample. We
conclude that the MAE is determined by the chemical disorder rather than by
lattice distortion.
