Unconventional ferromagnetic and spin-glass states of the reentrant spin glass Fe0.7Al0.3

Spin excitations of single crystal Fe0.7Al0.3 were investigated over a wide range in energy and reciprocal space with inelastic neutron scattering. In the ferromagnetic phase, propagating spin wave modes become paramagnon-like diffusive modes beyond a critical wave vector q0, indicating substantial disorder in the long-range ordered state. In the spin glass phase, spin dynamics is strongly q-dependent, suggesting remnant short-range spin correlations. Quantitative model for S(energy,q) in the ``ferromagnetic'' phase is determined.Comment: 4 pages, 5 figure

Depletion and voids formation in the substrate during high temperature oxidation of Ni-Cr alloys

A numerical model to treat the kinetics of vacancy annihilation at the metal/oxide interface but also in the bulk metal has been implemented. This was done using EKINOX, which is a mesoscopic scale 1D-code that simulates oxide growth kinetics with explicit calculation of vacancy fluxes. Calculations were performed for high temperature Ni-Cr alloys oxidation forming a single chromia scale. The kinetic parameters used to describe the diffusion in the alloy were directly derived from an atomistic model. Our results showed that the Cr depletion profile can be strongly affected by the cold work state of the alloy. In fact, the oversaturation of vacancies is directly linked to the efficiency of the sinks which is proportional to the density of dislocations. The resulting vacancy profile highlights a supersaturation of vacancy within the metal. Based on the classical nucleation theory, the possibility and the rate of void formation are discussed

X-ray spectrometer for anomalous scattering experiments : tests of a graphite mosaïc and a germanium monocrystal as analyzers

Anomalous X-ray scattering provides a useful way for improving the contrast between different atoms present in multi-element samples. To take full advantage of this technique, the detector has to have a good energy resolution in the diffracted beam to separate the elastic scattering signal from the inelastic one due to fluorescence or resonant Raman scattering (RRS). Solid state detectors are usually used, but the energy resolution is limited to about 150 eV which does not allow the separation RRS from elastic scattering. Ice and Sparks [ l ] described a mosaic crystal spectrometer which resolves this problem. We have adapted their setup on our beam line D23A at LURE-DCI but we have encountered a loss of resolution when the Bragg planes of the sample are inclined. The shape of the diffracted beam incoming on the position-sensitive detector depends strongly on the inclination of the diffracting planes ; this explains the loss of resolution which is increased in our case by the large horizontal incoming beam size. Alternatively, we recommend the use of a perfect crystal as an analyzer coupled with a 0d detector which gives a very good resolution (≈10eV) without modification of resolution when Bragg planes of the sample are inclined in X. Furthermore this kind of spectrometer allows a high counting rate so that it is possible to measure close to Bragg peaks (clustering studies, for example) and even Bragg peaks. The loss of efficiency is not dramatic considering the high brightness of third generation synchrotron radiation and is more than compensated by the improved signal to noise ratio

MAGNETIC FIELD DEPENDENCE OF STATIC CORRELATIONS AND SPIN DYNAMICS OF REENTRANT SPIN GLASSES STUDIED BY NEUTRON SCATTERING

We report small angle (SANS) and inelastic neutron scattering in zero and applied field for a-FeMn, NiMn and AuFe at composition where both ferromagnetic and frustration characters occur. We discuss the field evolution of the transverse correlations which arise below Tc. A study of the field dependence of the spin wave anomalies in a-Fe-Mn is reported

Interfacial structure and giant magnetoresistance in Fe/Cr superlattices

A correlation between interfacial structure and giant magnetoresistance (GMR) has been established for Fe/Cr superlattices [l-8]. However, previous studies were qualitative in that the interfacial structural disorder was expressed in terms of growth temperature, sputtering pressure or annealing temperature. In order to understand more quantitatively the effects of interfacial structure on GMR, we have undertaken [9] parallel measurements of x-ray diffraction (XRD) and magnetoresistance for two Fe/Cr samples subjected to a series of anneals at successively higher temperatures, both samples having initial GMR > 50 %. Such anneals are known to increase the thickness of the Fe/Cr interface through atomic diffusion, a structural change which can be characterized quantitatively by XRD. The advantages of high intensity and anomalous dispersion provided by synchrotron radiation has greatly contributed to the quality of our x-ray data, for which the use of simulation programs has allowed a robust and precise extraction of several structural parameters for the two samples, including the Fe/Cr interfacial thicknesses

Oscillatory interlayer exchange and magnetoresistance in Fe/Cu multilayers

We have studied the magnetic and magnetotransport properties of Fe/Cu mu1tilayers prepared by sputtering. We find oscillations of the inter1ayer coupling as a function of the Cu thickness with the same long period as in Co/Cu multilayers (around 12.5 Á). The most striking result is that the oscillations in Fe/Cu and Co/Cu have almost exactly opposite phases. A large magnetoresistance of the spin-valve type is observed in the half periods with antiferromagnetic interlayer exchange. However, the magnetoresistance in Fe/Cu is definitely smaller than in Co/Cu

Characterization of an aluminum conductor steel reinforced (ACSR) after 60 years of operation

International audienceAn aluminum conductor steel reinforced (ACSR) extracted from an overhead power line operated in Northern France during more than 60 years was characterized together with a more recent equivalent conductor. Visual inspection, local observation and chemical analysis by Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) as well as Raman spectroscopy were used to characterize the microstructure of the strands and to evidence signs of corrosion or potential degradation. Analysis of the grease was done by Fourier Transform InfraRed Spectroscopy (FTIR). The mechanical properties of the strands were evaluated by constant strain rate tensile test at ambient temperature. Hardness was measured as well. Partial oxidation of the steel galvanization layer, degradation of the grease – especially oxidation due to ageing – and atmospheric corrosion pits on the external layer of aluminum strands were evidenced. The mechanical properties of the galvanized steel strands were still in agreement with the requirements of the standards edited in 1955 contrarily to the mechanical properties of the external layer aluminum strands, indicating a potential deleterious effect of the corrosion pits. The tensile strength of the conductor estimated from the mechanical properties of its constitutive strands was slightly higher than the requirements of the standards edited in 1955 and slightly lower than the more demanding requirements of recent standard

Superconducting Polycrystalline Silicon Layer Obtained by Boron Implantation and Nanosecond Laser Annealing

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Synthesis of mono disperse magnetic nanoparticles prepared on block copolymer templates for medical imaging techniques

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