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The connection between the onset of ferromagnetism with an onset of magnetic anisotropy is examined. Ferromagnetic long-range order and uniaxial magnetic anisotropy appear for T >0 above a critical thickness of 2.5 ML suggesting the strong correlation between the onset of ferromagnetism and of magnetic anisotropy for Fe on GaAs(001).

The relation between the strong uniaxial magnetic anisotropy of Fe/GaAs(001) with the specific GaAs(001) surface reconstruction is examined. The easy axis of the uniaxial anisotropy is found along [110] in Fe(001) films grown by molecular-beam epitaxy on Ga-rich GaAs(001) surfaces at room temperature.

It has been possible to grow expitaxial Fe films ranging in thickness from 4 to 64 monolayers by molecular beam epitaxy on GaAs(110) at room temperature. It was found that, with decreasing temperature, the magnetic anisotropy in the films appeared to become more bulk-like.

It has been possible to grow ultrathin Fe films epitaxially at room temperature on GaAs(001) with either predominant (4x2) or (2x6) surface reconstruction. The onset of ferromagnetism was shown at a nominal Fe coverage of 2.5 monolayers.

Epitaxial Fe(sub 34)Co(sub 66) films in a thickness range from 3 to 100 monolayers (MLs) were grown by molecular beam epitaxy on GaAs(100) at room temperature. The growth was characterized by reflection high energy electron diffraction and x-ray diffraction.