Ab initio studies on the magnetic phase stability of iron

The possible collinear magnetic configurations of the α- and γ-Fe phases have been analyzed using the full-potential linearized augmented plane wave (FLAPW) method and the fixed spin moment (FSM) procedure in order to perform total energy and moment calculations, with which the phase stability could be checked. In the FSM, after the electronic configuration has been self-consistently determined, the resulting energy E is a minimum at the fixed total magnetic moment M per unit cell and volume per atom V. Subsequently, M should be changed through previously chosen steps, in order to get the E(M) curve for a given V. The minima of the curves at a given V represent the true magnetic phases of the system. From our calculations, the so-called AF-II antiferromagnetic phase, which requires a four-atom unit cell to exist, is the collinear ground state of γ-Fe, while for α-Fe the well-known ferromagnetic ground state is found. At some volumes, a crossing or degeneration of two or more magnetic phases appears. This may be regarded as an indication of a true non-collinear magnetic ground state of the system that remains to be studied. Nevertheless, experimental work seems to support that a collinear ferromagnetic arrangement is the ground state of the γ-Fe precipitates present in Fe–Cu mechanically alloyed solid solutions.