Matrix effect on order-disorder phase transition of FePt nanoparticles

A theoretical model is developed to systematically study the effect of the matrix on the order-disorder phase transition of FePt nanoparticles, which shows a significant role of the matrix or substrate to the ordering kinetics of FePt nanoparticles during the annealing process. It is shown that there exists a temperature window where one can obtain ordered FePt phase, while the high temperature limit with the largest nucleation rate is favorable for the formation of ordered FePt phase (L10). The matrix or substrate not only reduces particle agglomeration and sintering, but also increases the high temperature limit as well as nucleation rate. Furthermore, the effect of the matrix to the ordering kinetics of FePt nanoparticles relies on its surface energy, the higher the surface energy of the matrix is, the more pronounced the effect is. The validity of the present model is supported by as well the explanations of the contradiction results as the good agreement between the model predictions and experimental data. Those findings are very interesting and crucial for practical application when synthesizing ordered FePt nanoparticles.