ORIGIN OF THE UNIAXIAL MAGNETIC-ANISOTROPY IN FE FILMS GROWN BY MOLECULAR-BEAM EPITAXY

We report the observation of a weak in-plane uniaxial magnetic anisotr opy in Fe thin films grown by molecular beam epitaxy onto (001)-orient ed MgO substrates. This anisotropy has been observed both in (Fe/Pd) s uperlattices and in single epitaxial Fe layers within a large range of thicknesses (15-800 Angstrom). We find that the uniaxial anisotropy r esults from the geometry of the deposition system, and in particular f rom the angle of incidence of the Fe atomic flux during deposition. De tailed magnetic and structural studies of a 800 Angstrom thick single Fe layer show that this anisotropy can be explained as a volume effect resulting from the magneto-elastic energy associated with an in-plane tetragonal distortion of the cubic Fe structure, with (a-b)/a=+(1.2+/ -0.3)x10(-3).