Ground state magnetic properties of ultrathin fcc Fe and Co films on Cu(001) surfaces

The oxidation characteristics of silicon implanted with a low dose of nitrogen (1–3×10¹⁵cm^–2) have been studied for dry oxidation conditions at 1020°C. The wafers were subjected to a pre-oxidation annealing. Complete inhibition of the oxide growth occurs in the initial stage of oxidation, while the oxidation rate for prolonged oxidation is identical to that for pure silicon. The oxidation resistance increases with the implantation dose. The resistance is attributed to the formation of a nitrogen-rich surface film during annealing. This layer, which consists of only a few monolayers, is presumably composed of oxynitride. The electrical characteristics of MOS capacitors formed on implanted wafers show that the interface state density is not significantly increased by the low-dose N implantation.     

Development of magnetic anisotropies in ultrathin epitaxial films of Fe(001) and Ni(001)

Ultrathin films, bcc Fe(001) on Ag(001), fcc Fe(001) on Cu(001) and Fe/Ni(001) bilayers on Ag, were grown by molecular beam epitaxy. A wide range of surface science tools were employed to establish the quality of epitaxial growth. Ferromagnetic resonance and Brillouin light scattering were used to extract the magnetic properties. Emphasis was placed on the study of magnetic anisotropies. Large uniaxial anisotropies with easy axis perpendicular to the film surface were observed in all ultrathin structures studied. These anisotropies were particularly strong in fcc Fe and bcc Fe films. In sufficiently thin samples the saturation magnetization was oriented perpendicularly to the film surface in the absence of an applied field. It has been demonstrated that in bcc Fe films the uniaxial perpendicular anisotropy originates at the film interfaces. In situ measurements indentified the strength of the uniaxial perpendicular anisotropy constant at the Fe/vacuum, Fe/Ag and Fe/Au interfaces asK _us = 0.96, 0.63, and 0.3 ergs/cm² respectively. The surface anisotropies deduced for [bulk Fe/noble metal] interfaces are in good agreement with the values obtained from ultrathin films. Hence the perpendicular surface ansiotropies originate in the broken symmetry at abrupt interfaces. An observed decrease in the cubic anisotropy in bcc Fe ultrathin films has been explained by the presence of a weak 4th order in-plane surface anisotropy,K _1S=0.012 ergs/cm². Fe/Ni bilayers were also investigated. Ni grew in the pure bcc structure for the first 3–6 ML and then transformed to a new structure which exhibited unique magnetic properties. Transformed ultrathin bilayers possessed large inplane 4th order anisotropies far surpassing those observed in bulk Fe and Ni. The large 4th order anisotropies originate in crystallographic defects formed during the Ni lattice transformation.     

Surface structure of ultrathin Fe films on Cu(001) revisited

The structure and magnetism of ultrathin Fe films epitaxially grown on a Cu(001) surface are investigated by grazing scattering of fast H and He atoms or ions. By making use of a new variant of ion beam triangulation based on the detection of the number of emitted electrons, we obtain direct information on the structure of the film surface. We observe for room temperature growth a dominant and defined fcc-like structure. Complex surface reconstructions as reported in recent STM and LEED studies are observed only for cooling and H2 dosing.     

Ion beam triangulation of ultrathin Mn and CoMn films grown on Cu(001)

Total target currents for grazing scattering of keV protons from a crystal target are used to investigate the structure of surfaces and ultrathin films. This current shows pronounced maxima whenever the azimuthal incidence angle coincides with close-packed rows of atoms in the surface and subsurface layers. The real-space method is applied to study monolayer and bilayer films of Mn and of CoMn epitaxially grown on a Cu(001) surface.     

Temperature dependence of the surface anisotropy of Fe ultrathin films on Cu(001)

We report an experimental approach to separate temperature dependent reversible and irreversible contributions to the perpendicular magnetic anisotropy of Fe films grown at low temperatures on Cu(001) substrates. The surface anisotropy K(S)(T) is found to decrease linearly with temperature, causing a thermally induced spin reorientation into the plane. The irreversible shift of the spin reorientation transition and the coercivity of the iron films are directly correlated to the increasing Fe island size during annealing. The increased coercivity is discussed in terms of domain wall energy inhomogeneities provided by the islands.     

Structural and magnetic properties of ultrathin epitaxial Fe films on GaAs(001) and related semiconductor substrates

This article presents a review of the structural and magnetic properties of ultrathin epitaxial Fe films on GaAs(001) and related semiconductor substrates. Interest in these systems and Fe/GaAs(001) in particular has increased significantly over the last two decades, largely due to the emergence of the field of magnetoelectronics. Since then numerous studies of molecular beam epitaxy of Fe on GaAs(001) have been carried out, making it by far the best researched Fe/semiconductor(001) system. Issues such as magnetic anisotropy in the ultrathin regime, however, remain controversial with contradictory reports in the literature giving rise to considerable controversy within the field. By carefully scrutinizing the enormous amount of literature published on Fe/GaAs(001) so far and analysing these results within the wider context of Fe/semiconductor(001) systems, this article tries to settle some of these controversial issues, hence providing a long overdue ‘common denominator' for research in this area.     

MOCVD growth, structure and magnetic properties of Fe films grown on GaAs (001) substrates

Thin iron films have been grown on (001) GaAs substrates by low pressure metal organic chemical vapor deposition (LP-MOCVD) at different temperatures with the pressure of 150 Torr. X-ray diffraction (XRD) analysis showed that all films have only one strong diffraction peak (110). The surface of Fe film became smooth with increasing the growth temperature. Magnetization measurements showed that the Fe films grown at different temperatures were ferromagnetic with easy axis parallel to the film surface and hard axis perpendicular to the substrates. The field dependence of magnetization along two axes showed a remarkable difference, implying that the samples have strong magnetic anisotropy. Furthermore, when the applied magnetic field is perpendicular to the Fe surface, a sharp jump in the hysteresis loop could be observed, followed by a broad shoulder, which is related to the interface effect, the existence of carbon and the formation of 180^°/90^° magnetic domains.