The effect of magnetism on Fe diffusion: New experimental results and ab-initio calculations

摘要

Diffusion of non-magnetic impurities in a-Fe has been studied in an extended temperature range, using Ion Beam techniques. In all cases linear Arrhenius plots were obtained in the paramagnetic region, with a break at the Curie temperature (1043 K) and an up-ward curvature in the ferromagnetic region. This behavior is explained in terms of progressive lattice stiffness due to the alignment of the magnetic spins, as in the self-diffusion case. The maximum increment in the activation energy due to the ferromagnetic alignment (that corresponding to 0 K) is almost the same for all the non-magnetic diffusers, around 40 kJ/mol. The conservation of that quantity is also obtained from calculations using the WIEN97 code, which is an implementation of the linearized augmented plane wave (FP-LAPW) method based on density functional theory. In this paper the model is successfully applied to new measurements of As diffusion in ferromagnetic a-Fe. In consequence, such kind of diffusers can be considered as "magnetic vacancies" in the ferromagnetic lattice and the diffusion coefficient at low temperatures of other non-magnetic impurities can be extrapolated from the paramagnetic high temperature region and vice versa.