Large surface anisotropies in ultrathin films of bcc and fcc Fe(001) (invited)

Abstract

Large uniaxial anisotropies associated with interfaces are observed for ultrathin films (3-28 ML) of bcc Fe(001) grown epitaxially on Ag(001) single-crystal substrates and for epitaxial sandwiches of fcc Fe(001) grown with three layers of Fe using Cu as substrate and coverlayers. The uniaxial anisotropy is well described by a pseudosurface anisotropy term as theoretically predicted, yet that theory also predicts large in-plane anisotropies that are not observed. Adequate treatment of spin-orbit coupling in magnetic theories remains a challenge. Comparisons of ultrathin films of bcc Fe(001) on Ag(001) with different coverlayers of Ag or Au show subtle differences in magnetic behavior as studied by ferromagnetic resonance (FMR) and Brillouin light scattering (BLS). The FMR measurements were carried out at 9.6, 36.6, and 73 GHz microwave frequencies. The BLS measurements were performed using a six-pass Fabry–Perot interferometer. The power of the techniques of molecular-beam epitaxy (MBE) for producing well-characterized interfaces is stressed. Growths at 140 K are compared with those at 300 K to show the limited role of interdiffusion. Oscillations in the intensity of reflection high-energy electron diffraction (RHEED) are exploited in the characterization of growth. Comparison of the properties of films grown on perfect iron whisker surfaces with results for mosaic single-crystal substrates show that, while the former are much to be preferred for growth studies, the latter are really adequate for magnetic studies.