Uniaxial magnetic anisotropies in Fe films on single crystal and virtual Ge(001) substrates studied with spin polarized inverse photoemission and MOKE

Abstract

Fe films have been grown at room temperature on standard Ge(001) single crystals and virtual $\mathrm{Ge}∕{\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}∕\mathrm{Si}(001)$ substrates, and their magnetic properties extensively investigated in situ by spin polarized inverse photoemission and magneto-optical Kerr effect. Two different uniaxial anisotropies have been found to coexist. The first one, giving rise to a [110] easy axis, is associated to the $\mathrm{Fe}∕\mathrm{Ge}$ interface: it disappears at large thickness (more than 10 Fe layers), while dominates in very thin films (5 Fe layers) on virtual substrates. A second anisotropy, considerably smaller in strength, originates a [010] or [100] easy axis: it persists at large thickness (up to 60 Fe layers) and is essentially associated to bulk properties. However, this is not an intrinsic property, being related to the sample preparation conditions, i.e., substrate sputtering at oblique incidence for cleaning and Fe deposition at oblique incidence. The uniaxial easy axis is always perpendicular to the incidence plane, either of the Fe atoms flux or the ion beam, with a larger effect of deposition conditions with respect to sputtering. Our results give evidence of a strong correlation between morphology and magnetism in $\mathrm{Fe}∕\mathrm{Ge}∕{\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}∕\mathrm{Si}(001)$ and $\mathrm{Fe}∕\mathrm{Ge}(001)$ films, opening the way to the engineering of magnetic properties via the control of the preparation conditions.