FOURFOLD ANISOTROPY AND STRUCTURAL BEHAVIOR OF EPITAXIAL HCP CO GAAS(001) THIN-FILMS/

Thin Cr-capped Co films (thickness 50-150 Angstrom) have been grown ep itaxially on GaAs(001) single-crystal substrates by molecular-beam epi taxy. In contrast to other investigations, transmission electron diffr action reveals that the epitaxial Co films have a hexagonal-close-pack ed (hcp) structure with the epitaxial relationships ((1) over bar 2 (1 ) over bar 0)[0001]Co parallel to(001)[110]GaAs and ((1) over bar 2 (1 ) over bar 0)[0001]Co parallel to(001)[(1) over bar 10]GaAs, i.e., the c axis of each crystallite is assigned to either the in-plane [110] o r the [<(1)over bar10] direction of the GaAs(001) substrate. In-plane magneto-optical Kerr-effect hysteresis loops and Brillouin light-scatt ering measurements show that the thinnest epitaxial hcp Co film (50 An gstrom) has a dominant fourfold anisotropy with easy axes along the in -plane [100] directions and that a uniaxial anisotropy becomes dominan t with increasing film thickness. We are able to account for the magne tic anisotropy properties of these epitaxial Co films in terms of thei r oriented hcp microstructure.