Atomic Diffusion in $\alpha$-iron across the Curie Point: An Efficient and Transferable Ab Initio–Based Modeling Approach

An accurate prediction of atomic diffusion in Fe alloys is challenging due to thermal magnetic excitations and magnetic transitions. We propose an efficient approach to address these properties via a Monte Carlo simulation, using ab initio–based effective interaction models. The temperature evolution of self- and Cu diffusion coefficients in $\alpha$-iron are successfully predicted, particularly the diffusion acceleration around the Curie point, which requires a quantum treatment of spins. We point out a dominance of magnetic disorder over chemical effects on diffusion in the very dilute systems.

Figure 1

Left panel: Magnetic free energy, enthalpy, and entropy of formation. Right panel: Magnetic free energy, enthalpy, and entropy of migration.

Figure 2

Upper-left panel: Self-diffusion coefficients of Fe versus $T$, with and without quantum effects and comparison with experimental data obtained from Refs. [1, 2, 3, 4, 5, 7, 8, 10]. Bottom-left panel: Diffusion coefficients of Fe and Cu, compared with experimental results, obtained from Refs. [1, 2, 3, 4, 5, 7, 8, 10] for Fe and Refs. [4, 14, 67] for Cu. Upper-right panel: Kinetic correlation factors of Fe self-diffusion ($f0$) and Cu diffusion ($f2$). The $f2$ kinetic correlation with the frozen FM state (see the text) is also displayed. Bottom-right panel: Migration magnetic free energies of various jumps.

Figure 3

Activation, formation, and migration free energies compared with the Ruch model.