Ab Initio Calculation of Phase Boundaries in Iron Along the bcc-fcc Transformation Path and Magnetism of Iron Overlayers

A detailed theoretical study of magnetic behavior of iron along the bcc-fcc (Bain’s) transformation paths at various atomic volumes, using both the local spin-density approximation (LSDA) and the generalized gradient approximation (GGA), is presented. The total energies are calculated by the spin-polarized full-potential linearized augmented plane waves method and are displayed in contour plots as functions of tetragonal distortionc/aand volume; borderlines between various magnetic phases are shown. Stability of tetragonal magnetic phases of γ-Fe is discussed. The topology of phase boundaries between the ferromagnetic and antiferromagnetic phases is somewhat similar in LSDA and GGA; however, the LSDA fails to reproduce correctly the ferromagnetic bcc ground state and yields the ferromagnetic and antiferromagnetic tetragonal states at a too low volume. The calculated phase boundaries are used to predict the lattice parameters and magnetic states of iron overlayers on various (001) substrates.