Magnetic behavior of Fe sites in Fe-Mo-Al alloys: The role of the first neighborhood

We analyse the influence of the nearest neighborhood on the magnetic behaviour at Fe sites in bcc-based Fe-Al, Fe-Mo and Fe-Al-Mo alloys. Theoretical ab initio calculations were performed in the framework of the Density Functional Theory using the Full Potential-Linear Augmented Plane Wave method as embodied in the WIEN97 code. The analysis is made through local magnetic moments considering the distribution of the first coordination shell of the Fe atoms. We find that the magnetic moment is nearly independent of the composition in the Fe-Mo binary. Although the magnetic behaviour of Fe-Al alloys is a very complex and controversial subject, our results clearly show that an increase in the number of Al nearest neighbours leads to a decrease or even to the suppression of the local moment at Fe sites. On the other hand, the ternary bcc-based Fe-Mo-Al alloys present no correlation between magnetism and the composition of the nearest neighbor shell. The results are discussed in connection with their implications for the thermodynamic modelling of magnetism in the CALPHAD approach.