Ph. Mangin

Epitaxial growth of (110) DyFe2, TbFe2 and Dy0.7Tb0.3Fe2 thin films by molecular beam epitaxy

We present the first epitaxial growth of some (110) rare earth-Fe2 (DyFe2, TbFe2 and Dy0.7Tb0.3Fe2 known as terfenol-D) thin films on (110) Nb(11−20) sappire by molecular beam epitaxy. The epitaxy is initiated by the deposition of a thin layer of iron on niobium. The structures are investigated by RHEED and X-ray scattering. Depending on the thermal treatment of the iron thin layer, the films of RE-Fe2, epitaxially grown on it, are either single crystals or present twins related by a 110° rotation about the surface normal. The growth of epitaxial thin films of these compounds is of interest because of the magnetic and magnetostrictive properties these materials may exhibit.

Magnetism in amorphous Fe-Si alloys

Abstract Fe-Si alloys have been obtained by the vapor quenching technique. Resistance measurements, electron microscopy and diffraction results are typical of an amorphous system. The Mossbauer spectra of these amorphous alloys, fitted in terms of a distribution of hyperfine fields, show the existence of a local magnetic order with, however, a proportion of weakly or even no coupled Fe atoms which is temperature and Fe-concentration dependent.

Structural description of iron-silicon amorphous alloys

Abstract Typical Fe x Si1-x amorphous alloys have been studied by electron diffraction and resistivity measurements in a wide concentration range (0 ≤ x ≤ 0·75). A description of the short-range order in these systems is proposed in terms of a dense random packing of hard spheres, as in pure amorphous metals, if x ≥ 0·3. In the small iron concentration range (x ≤ 0·2) the structure becomes progressively similar to an amorphous semiconductor, as pictured by a continuous random network model. Iron and silicon atoms appear to be distributed without chemical correlations.

Crystal growth and precipitation in thin films of amorphous Fe–Au alloys

Abstract Metastable alloys of the Fe–Au system have been prepared by the vapour quenching technique. The films so obtained are studied by resistivity measurements and by transmission electron microscopy and diffraction. Alloys containing more than 60 at. % Fe are amorphous at low temperature and a transformation to a metastable b.c.c. solid solution occurs at a temperature ranging from 80 to 250 K when the concentration varies from 80 to 60 at. % Fe. A further annealing at higher temperature leads to the precipitation of a gold-rich f.c.c. phase which grows, in a platelet structure, from linear defects formerly observed in the metastable b.c.c. phase. Kinetic parameters of the crystallization and orientation relationship between the phases during the precipitation are determined.

Evidence for Antiferromagnetic Coupling in Ag/Ni Superlattices: a Neutron Scattering Study

Low-angle neutron scattering experiments in reflection geometry have been performed on Ag/Ni superlattices prepared by sputtering. The low-temperature diffraction diagram shows the appearance of a supplementary low-angle peak attributed to the doubling of the chemical period, as a consequence of the antiparallel alignment of the magnetic moments in successive nickel layers. The variation of the intensity of this antiferromagnetic peak with applied magnetic field is in accordance with a classical model of antiferromagnetism in which the magnetic moments, at first perpendicular to the field, rotate progressively to the direction of the field. A good agreement is found with magnetization and magnetoresistance results obtained on the same samples.

Magnetic measurements on amorphous FeSi alloys

Magnetisation measurements on FexSi1-x amorphous alloys show the existence of a critical concentration at x=0.4. On the other hand the magnetic behaviour seems to be quite similar to the one observed in crystallised solid solution.

Crystallization of Au x Si1−x amorphous alloys

Abstract Amorphous Au x Si1−x alloys have been prepared by vapour deposition at 77 K over a wide range of composition (0  x  0·80). Crystallization has been studied by electrical resistivity measurements, electron microscopy and diffraction. A metastable crystalline phase μ is formed before reaching the equilibrium dissociation into crystalline gold and silicon. This metastable phase has a composition near Au3Si and may be obtained alone or in a mixture with silicon depending on the amorphous alloy composition. Short-range order in the amorphous material is discussed with respect to the structure of the μ phase. It is suggested that amorphous alloys appear to exist as a single phase only at the Si-rich end of the composition range and near the eutectic composition.

Magnetoelastic and Exchange Contributions to the Helical-Ferromagnetic Transition in Dysprosium Epitaxial Films

The Curie temperature of dysprosium films epitaxially grown on yttrium and on erbium is shown to increase continuously with the epitaxial strain induced along the c-axis. This variation is correlated to modifications of the α strains, of the γ distortion and of the exchange energy barrier. The evolution of these different terms is discussed from the experimental thermal variations of the lattice parameters and turn angles determined by neutron diffraction.

Neutron-diffraction study of hydrogenated and deuterated CuTi amorphous alloys

Neutron-diffraction experiments have been performed on amorphous CuxTi1-x (x=0.67,0.50,0.35) alloys charged either with hydrogen or deuterium. The variation of the interference functions and pair-correlation functions have been studied as a function of copper and hydrogen or deuterium concentration. The results obtained of non-hydrogenated alloys confirm the existence of chemical order. First-neighbour distances are determined and can be well compared with those in corresponding crystalline phases. The good contrast between copper and titanium on the one hand and between hydrogen and deuterium on the other allows one to identify individual metal-hydrogen correlations. Their positions in the total pair-correlation functions are very close to those found in crystalline hydrides and show that Ti3 tetrahedra are preferred hydrogenation sites in the concentration range studied.

Structural and magnetic profiles in Fe/Si multilayers

Abstract Iron-silicon multilayers were prepared by vacuum evaporation and characterized by cross-sectional electron microscopy, electron diffraction, in situ electrical measurements and low-angle X-ray scattering. Mossbauer spectroscopy measurements carried out on samples with different silicon and iron thicknesses showed a distribution of the magnetic moments of the iron atoms. The Mossbauer spectra are analysed with reference to those of Fe-Si amorphous and crystalline alloys. They show iron atoms in a pure bcc crystalline phase, in a bcc crystalline phase with a silicon atom as a first neighbour, in an amorphous magnetic phase with a large hyperfine field distribution and in an amorphous non-magnetic phase. A Jaccarino-Walker type hypothesis allows us to propose a model for structural and magnetic profile of the layers which is consistent with neutron scattering and Mossbauer spectroscopy data.