  The aim of this work is to investigate the structural and magnetic
characteristics of Fe thin films with a triangular (hexagonal) lattice surfaces
(fcc (111) and bcc (111)). The properties of these structures have been
calculated using density functional theory (DFT) implemented in the
full-potential local-orbital(FPLO) code. The results indicate a structural
phase transition from fcc to bcc structure when the film thickness exceeds 23
Fe atomic monolayers. The considered fcc films prefer the low-spin
ferromagnetic state with an average magnetic moment of about 1.0 $\mu_{B}$ per
atom. This moment decreases with increasing film thickness until the critical
thickness, where, after the structural transition to the bcc phase, it reaches
a value close to that of bulk bcc Fe. Moreover, the values of the magnetic
anisotropy energy are positive (perpendicular magnetic anisotropy) for the
entire thickness range of films with fcc structure (in ferromagnetic low-spin
state) and systematically decrease with increasing film thickness. The
presented computational results explain the experimentally observed structural
transition and may help to select appropriate substrates with suitable lattice
parameters for the deposition of ultrathin Fe(111) films.
