Process-Induced Uniaxial Magnetic Anisotropy in Epitaxial Fe and Ni₈₀Fe₂₀ Films

Abstract

The occurrence of a weak in-plane uniaxial magnetic anisotropy in Fe thin films grown by molecular beam epitaxy onto (001)-oriented MgO substrates has been previously reported. We explain the occurrence of this anisotropy by measuring the in-plane tetragonal distortion of the cubic Fe lattice in a 800Å-thick film. The analysis of the full x-ray diffraction spectrum reveals a 0.1% difference between the two in-plane parameters. This small difference is sufficient to fully explain the observed anisotropy (≈20 Oe) using a standard magnetoelastic model. Although it is established that the uniaxial anisotropy results from the angle of incidence of the Fe atomic flux during deposition, the relationship between angle of incidence and in-plane tetragonalization is still unexplained. However, this anisotropy is shown to also occur in other epitaxial systems such as Ni₈₀Fe₂₀ on (111)Si. Control of this effect can help design epitaxial multilayer films with specific and reproducible magnetic states.