M. Piecuch

Magnetic and structural properties of iron nitride thin films obtained by argon‐nitrogen reactive radio‐frequency sputtering

We have prepared iron nitride thin films by reactive rf sputtering of an iron target in an argon‐nitrogen plasma. The films present a wide variety of structures and compositions: α expanded bcc iron, amorphous Fe1−x‐Nx, γ’‐Fe4N, e‐Fe2–3N, and ζ‐Fe2N. Evolutions of the crystallographic structures and of the magnetic properties of the obtained phases are discussed versus the nitrogen concentration in the gaseous flow and the substrate temperature during deposition.

Structure and short-range order of vapour-deposited Si1−xSnx amorphous alloys

Abstract Amorphous Si1−x Snx alloy films have been prepared by the simultaneous evaporation of Si and Sn in high vacuum onto various substrates held at liquid nitrogen temperature. The structure of the alloys was investigated using scanning high-energy electron diffraction, density measurements and Mossbauer spectroscopy. For x<0·5, Sn atoms are shown to be substituted for Si, and selectively surrounded by Si atoms in almost perfect tetrahedral units, in a random continuous network. This trend of the alloys towards order can be traced to the size difference between Si (d = 2·35 A) and Sn (d = 2·80 A).

FeIr(001) superlattices : growth, structure, and magnetic properties

The study of structures and magnetism of FeIr(001) superlattices leads us to observe three different cases. First, for Fe thicknesses up to 4 planes, Fe is of bct structure with an fcc Ni-like magnetic anisotropy. Second, for thick Fe layer, Fe is bcc and an antiferromagnetic coupling is observed. Third, for thin Ir layers, Ir is strained and plays an inportant role in magnetic behaviour.

Interdiffusion and chemical ordering in composition‐modulated Fe70Si30/Si amorphous thin films

The interdiffusivity and chemical ordering in compositionally modulated (Λ=20 to 40 A) amorphous Fe70Si30/Si thin films have been measured from the decay of the satellite intensities of the (000) x‐ray scattering peak during isothermal anneals in the temperature range 373–473 K. Diffusivities as low as 10−26 to 10−25 m2 s−1 have been measured. A linear dependence of DΛ on 1/Λ2 has been observed, providing the evidence of chemical ordering in Fe‐Si alloy and leading to the determination of a critical wavelength.

About the magnetic behaviour of FexMe1-x (Me=Si, Ge, Sn) amorphous alloys

Magnetisation measurements have been carried out in FexSn1-x amorphous alloys obtained by atomic deposition. A critical composition, xcr approximately=0.4, for the onset of ferromagnetism has been found along with a rapid increase of the magnetisation when x>xcr. Comparison with data previously obtained for FexSi1-x and FexGe1-x amorphous alloys suggests that the onset of magnetic ordering may result from localised interactions; details of the short-range order and chemical correlations might be quite different for Si, Ge and Sn compounds. Temperature dependence of the magnetisation has shown that there is not a well defined Curie temperature in amorphous FexSn1-x which is consistent with magnetic inhomogeneities.

Relaxation and diffusion study by small angle neutron scattering technique in amorphous semiconductor superlattices

Abstract Superlattices consisting of alternating layers of amorphous silicon and germanium have been studied using small angle scattering techniques with cold neutrons. From the behviour of the (000) forward scattering satellite during thermal treatment it has been possible to analyse structural relaxation in the system in terms of bulk compaction through the enhanced mobility of the interstitial-like defect. Real diffusion was not observed under the experimental conditions.

Structure and d.c. conductivity of amorphous Si1−xSnx alloys

Abstract Amorphous Si1−xSnx alloys have been prepared by vapor deposition at a pressure of about 10−8 Torr on substrates maintained at 77 K. Density measurements and electron diffraction show that Sn atoms are substituted for Si in a random continuous network. The d.c. resistivity of samples of stabilized structure is correctly described by the variable range hopping formula. Structural changes are revealed by the variation of the resistivity at 77 K of samples annealed from 77 K to the crystallization temperature.

Structural and magnetic properties of FeFe2N sputtered multilayers

Abstract We have prepared iron-iron nitride multilayers by sequential reactive-nonreactive sputtering. The structure of the FeFe 2 N interfaces has been studied and found to be correlated with the magnetic properties of such samples. They are found to remain sharp enough for direct observation of multilayers either by transmission electron microscopy or by small angle X-ray scattering despite a significant shift of the Fe(Fe,N) interfaces towards the iron layers as a result of nitrogen diffusion.

Resonant magnetic scattering in soft X-ray range using multilayers

Abstract X-ray resonant magnetic scattering experiments using linearly polarised light have been performed at the L 2,3 absorption edges of Co in a magnetically coupled Cu/Co multilayer. Taking advantage of the dependence of the scattering intensity on the magnetisation direction, we succeed in bringing out a purely magnetic peak due to the antiferromagnetic coupling between successive Co layers. Then for a ferromagnetically coupled multilayer, large changes in the scattering intensity of Bragg peaks of the multilayer (up to 45%) have been observed upon reversal of the direction of magnetisation in the multilayer.

Magnetic and transport properties of Ni/Ti, NiC/Ti and Co/Cu multilayers at high fields

Abstract We studied the magnetoresistance of Ni/Ti, NiC/Ti and Co/Cu sputtered multilayers. In fields below 2 T, the Co/Cu films exhibit previously described giant magnetoresistance. We observe an unusual negative contribution to the magnetoresistance in high fields whose origin is not well understood at this time.