Influence of substrate surface reconstruction on the growth and magnetic properties of Fe on GaAs(001)

We have studied the magnetic and structural properties of epitaxial bcc Fe(001) films grown at 175 degrees C on molecular-beam epitaxy-prepared GaAs(001)-2X4 and -c(4X4) reconstructed surfaces, with film thicknesses ranging up to similar to 30 ML (similar to 43 Angstrom). We present measurements of the thickness-dependent evolution of the magnetic properties of the Fe films as determined by in situ magneto-optic Kerr effect. We find that the magnetic properties and growth mode are similar for both 2X4 and c(4x4) reconstructions, although the initial adsorption sites and island nucleation as measured by scanning tunnelling microscopy are clearly dominated by the substrate surface reconstruction. The onset of room-temperature ferromagnetism occurs at 6 ML for growth on both GaAs surface reconstructions. At this coverage, the measured Curie temperature (similar to 100 degrees C) is significantly reduced from that of bulk alpha-Fe (770 degrees C). The anisotropy is dominated by a uniaxial component such that the two [110] axes are inequivalent for all coverages studied. Shape anisotropy does not appear to play a significant role.