KERR-EFFECT STUDY OF THE ONSET OF MAGNETIZATION IN FE FILMS ON GAAS(001)-2X4

We have studied the magnetic behavior of epitaxial bcc Fe(001) films g rown on molecular beam epitaxy-prepared GaAs(001)-2X4 substrates, with film thicknesses ranging up to similar to 16 monolayers (ML) (similar to 23 Angstrom). We present measurements of the thickness-dependent e volution of the magnetic properties of the Fe films as determined by i n situ magneto-optical Kerr effect. Particular attention is given to t he substrate-induced in-plane uniaxial magnetic anisotropy. We find th at the onset of room-temperature ferromagnetism occurs between 4 and 8 ML, and that the anisotropy is dominated by a uniaxial in-plane compo nent such that the two [110] axes are inequivalent for all coverages s tudied. Although the initial nucleation and growth results in 2D islan ds elongated along [(1) over bar 10], the in plane easy axis is perpen dicular to this direction along [110], indicating that shape anisotrop y does not play a significant role. (C) 1997 American Institute of Phy sics.