Chemisorbed halogen adlayers on Fe(110): Electronic band structure and surface geometry

A series of overlayer structures, starting with a c(3 × 1) geometry are formed during the dissociative chemisorption of chlorine, bromine, and iodine on Fe(110). These adlayers provide an opportunity to systematically examine the corresponding changes in electronic band structure as a function of coverage and adsorbate. At coverage levels greater than low-energy electron diffraction patterns obtained from the halogen-covered Fe(110) surface evolve continuously with coverage. The electronic band structure was examined as a function of coverage and adsorbate species via angle-resolved ultraviolet photoelectron spectroscopy. It is concluded that the electronic band structure measurements support an incommensurate structural model for halogen overlayer geometry on Fe(110) in which an overlayer lattice, that is in general incommensurate with the substrate, rotates and compresses with increases in coverage. An alternative interpretation of the diffraction results based on antiphase domain boundaries within the overlayer is not consistent with the photoemission data. The incommensurate model emphasizes adatom-adatom interactions over adatom-substrate interactions while the reverse is true for the antiphase boundary model.     

Magnetic coupling in Gd(Fe6−x Cr x )Al6: A57Fe Mössbauer study

⁵⁷Fe Mössbauer measurements have been made on the ternary ThMn₁₂-type intermetallic compounds Gd(Fe_6–x Cr _x )Al₆ withx=0, 0.5, 1.0, 1.5 and 2.0, at temperatures of 4.2 and 77 K. The principal effect of the Cr substitution is to reduce the⁵⁷Fe magnetic hyperfine field at 4.2 K in this series. The analysis of the⁵⁷Fe Mössbauer spectra is consistent with a ferromagnetic coupling between the Gd and Cr magnetic moments. These results are in agreement with previous studies by Felner et al. on GdCr₆Al₆, in which a ferromagnetic ordering withT _C=170 K was observed.On leave from Applied Acoustics Institute, Shaanxi Teachers University, Xian, PR China.     

Diffusion of N adatoms on the Fe(100) surface

The diffusion of individual N adatoms on Fe(100) has been studied using scanning tunneling microscopy and ab initio density functional theory (DFT) calculations. The measured diffusion barrier for isolated N adatoms is E(d) = (0.92+/-0.04) eV, with a prefactor of nu(0) = 4.3x10(12) s(-1), which is in quantitative agreement with the DFT calculations. The diffusion is strongly coupled to lattice distortions, and, as a consequence, the presence of other N adatoms introduces an anisotropy in the diffusion. Based on experimentally determined values of the diffusion barriers and adsorbate-adsorbate interactions, the potential energy surface experienced by a N adatom is determined.     

Magnetic and structural properties of Fe(110)/Ag(111) and Fe(100)/Ag(100) multilayers

A comparison of the magnetic and structural properties and growth characteristics between Fe(110)/Ag(111) and Fe(100)/Ag(100) multilayers is presented. The two types of multilayers were made of the same constituent materials but with different oricutations, allowing us to examine the interesting interplay between structure and magnetism. We found fundamentally different magnetic properties including magnetocrystalline anisotropy and surface/interface and thin film magnetism for the two types of multilayers, and their origins were discussed. Presently at the Naval Research Laboratory. Presently at Argonne National Laboratory.     

Magnetic properties of Fe and Co nanoclusters embedded in the first Cu(100) surface layer

The magnetic anisotropy energies, as well as spin and orbital magnetic moments of the atoms involved in the simplest nanostructures formed due to the self-organization within the first Cu(100) surface layer, are calculated in the framework of the density functional theory. The critical role of the surface relaxation, which leads to the rotation of the easy magnetization axis in iron nanoclusters, is demonstrated in the calculations of magnetic anisotropy.     

Magnetic properties of 57Fe/Ir(100) superlattices

Summary The synthesis of a new BCT Fe phase was performed in Fe/Ir(100) superlattices grown by MBE. Magnetic properties of⁵⁷Fe/Ir(100) superlattices with 4 ml Fe and variable Ir thickness (2–30 ?) are investigated by⁵⁷Fe conversion electron M?ssbauer spectroscopy in the 4.2–300 K temperature range. Two spectral components are evidence, related, respectively, to Fe atoms involved in the central part of the iron layers and at the interface between iron and iridium layers. The appearance of a high magnetic hyperfine splitting in the iron BCT structure above a volume threshold of 12 ?³ is evidenced. Marked differences are observed between the mean magnetic properties and the local ones suggesting strong relaxation effects. Paper presented at ICAME-95, Rimini, 10–16 September 1995.