A. R. Ross

Structural transformations in quenched Fe–Ga alloys

Abstract It has been speculated that the large increase in magnetostriction in Fe–Ga alloys results from local short-range ordering of the Ga atoms along specific crystallographic directions in the disordered Fe structure. The structural transitions associated with different cooling rates from the high temperature disordered state were investigated with X-ray diffraction of oriented single crystals of Fe–19 at% Ga. Results are presented for long-range ordering during slow cooling and indirect evidence of local short-range ordering of Ga atoms in the disordered state when the alloys are quenched is also presented. In the latter case, the short-range ordering of Ga atoms leads to a tetragonal distortion of the lattice. The dependence of the magnetostrictive response of Fe–Ga alloys on thermal history has been found to be directly related to these structural transformations in Fe–19 at% Ga alloys and experimental support for the proposed magnetostriction model based on Ga–Ga pairing along [100] crystallographic directions is presented.

Pseudomorphic Growth of a Single Element Quasiperiodic Ultrathin Film on a Quasicrystal Substrate

Surface Science Research Centre and Department of Physics,The University of Liverpool, Liverpool L69 3BX, UKWe have synthesised a thin film of copper with a quasi-periodic structure by the adsorption ofcopper atoms on the five-fold surface of the icosahedral quasicrystal Al-Pd-Mn at room temperature.The quasi-periodicity of the thin film is manifested in low energy electronic diffraction (LEED)measurements and in the existence of Fibonacci relationships between rows of copper atoms imagedusing scanning tunneling microscopy (STM). These findings demonstrate the feasibility of single-element quasi-periodic thin film formation using quasicrystals as templates.

Magnetostriction of ternary Fe–Ga–X alloys (X=Ni,Mo,Sn,Al)

Investigations were made into the effect of small additions of Ni, Mo, Sn, as well as larger additions of Al on the magnetostriction of single crystal Fe100−xGax alloys (x≅13). The Fe–Ga and Fe–Al systems are seemingly unique among the Fe-based alloys in having very large magnetostrictions in spite of Ga and Al being nonmagnetic. In this paper, we show how additions of Ni, Mo, Sn, and Al affect λ100 and λ111 of the binary Fe–Ga alloys. We substituted small amounts of Ni into a binary Fe–Ga alloy in an attempt to reduce the magnitude of the negative λ111, as Ni does in Fe, in order to improve the magnetostriction of polycrystals. The measured λ111’s were reduced to a very small value, ∼3 ppm, but λ100 fell dramatically to +67 ppm for Fe86Ga11Ni3. Mo was substituted for Ga to determine the effect of a partially filled 4d shell on the magnetostriction. Here |λ111| is affected the most, increasing to a value greater than all known α-Fe-based alloys (λ111=−22 ppm for Fe85Ga10.2Mo4.8). We find that the addition...

Pseudomorphic Starfish: Nucleation of Extrinsic Metal Atoms on a Quasicrystalline Substrate

Abstract Direct observation of extrinsic Al atoms on the fivefold surface of icosahedral Al–Cu–Fe indicates that they form pseudomorphic islands resembling starfish. The starfish occupy specific types of sites on the laterally-bulk-terminated quasicrystalline surface. We postulate that the nucleation event consists of a diffusing Al atom dropping into an empty site at the centre of a substrate pentagon. Growth consists of the addition of five Al atoms (nearly) in lattice sites. These 6-atom starfish do not grow laterally as coverage increases, leading to islands of uniform size, and to early roughening.

Quasicrystal surfaces: potential as templates for molecular adsorption

Abstract We report on investigations of the potential for using quasicrystal surfaces as templates for molecular adsorption. The quasicrystalline surfaces of the i -Al–Pd–Mn and the d -Al–Ni–Co quasicrystals have been dosed with various molecules and the surface reactivity characterised by Fourier transform infrared spectroscopy (FTIR). The reflected signal intensities obtained are much weaker than those obtained from other crystals such as metals. Although both quasicrystals are Al-based their surface reactivities are seen to differ. For the Al–Pd–Mn surface, NO and HCOOH both dissociate at the surface and CO does not adsorb. CD 4 O adsorption leads to multilayers as in other crystals. C 6 H 6 molecules stick at low coverages and at low temperatures whilst not affecting the LEED pattern. For the Al–Ni–Co surface, CO molecules stick via activated adsorption to atop sites with vibrational frequencies very similar to CO adsorption on Ni. HCOOH forms multilayers at low temperatures which is reduced to a monolayer upon heating to 173 K; changes in the symmetry of the bonding are observed, which is also seen for HCOOH on Ni surfaces. NO and CD 4 O showed no characteristic spectra, which may be due to dissociation or a very low sticking probability. We summarise these observations and draw some conclusions as to the most favourable route for molecular overlayer formation.

Adsorption of cobalt on the tenfold surface of d-Al72Ni11Co17 and on the fivefold surface of i-Al70Pd21Mn9

The adsorption behaviour of Co on the tenfold surface of d-Al72Ni11Co17 and on the fivefold surface of i-Al70Pd21Mn9 has been studied using scanning tunnelling microscopy (STM), Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). The analysis of a distinctive quasiperiodic LEED pattern for coverages from 3–30 ML of Co on d-Al72Ni11Co17 suggests that the Co forms in a pseudomorphic row structure composed of domains of Fibonacci spaced rows having a periodic lattice parameter along the rows of 2.5 ± 0.1 Å. The same structure, though less well-ordered and with a larger lattice parameter, is formed on the fivefold surface of i-Al70Pd21Mn9.

Nucleation and growth of a quasicrystalline monolayer: Bi adsorption on the fivefold surface of i-Al70Pd21Mn9

Scanning tunneling microscopy has been used to study the formation of a Bi monolayer deposited on the fivefold surface of

Angle-resolved low-energy ion scattering studies of quasicrystalline Al-Pd-Mn

i{\text{-Al}}_{70}{\text{Pd}}_{21}{\text{Mn}}_{9}

Determination of Auger sensitivity factors for Al-rich quasicrystals

. Upon deposition of low submonolayer coverages, the nucleation of pentagonal clusters of Bi adatoms of edge length

Structural studies of Fe0.81Ga0.19 by reciprocal space mapping

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