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J P Itié

Publications and source records attributed to J P Itié.

5 recordsLinked to original sources
PubMed2005

Magnetic instabilities in Fe3C cementite particles observed with Fe K-edge x-ray circular dichroism under pressure.

The ferromagnetic interstitial iron compound Fe(3)C (cementite) is expected to have Invar properties, whereby a high-moment to low-moment transition should occur when the atomic volume is reduced below a critical value. We, therefore, examine the pressure dependence of the Fe K-edge x-ray magnetic circular dichroism in Fe(3)C at ambient temperature and pressures up to 20 GPa. We find clear evidence for a high-moment to low-moment transition around 10 GPa.

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PubMed2004

Dynamics of the magnetic and structural alpha-epsilon phase transition in iron.

We have studied the high-pressure iron bcc to hcp phase transition by simultaneous x-ray magnetic circular dichroism and x-ray absorption spectroscopy with an x-ray energy dispersive spectrometer. The combination of the two techniques allows us to obtain simultaneously information on both the structure and the magnetic state of iron under pressure. The magnetic and structural transitions simultaneously observed are sharp. Both are of first order in agreement with the theoretical prediction. The pressure domain of the transition observed (2.4+/-0.2 GPa) is narrower than that usually cited in the literature (8 GPa). Our data indicate that the magnetic transition slightly precedes the structural one, suggesting that the origin of the instability of the bcc phase in iron with increasing pressure is to be attributed to the effect of pressure on magnetism as predicted by spin-polarized full-potential total energy calculations.

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PubMed2001

EXAFS study on liquid gallium under high pressure and high temperature.

EXAFS (Extended X-ray Absorption Fine Structure) spectra of liquid gallium near the Ga K-edge have been collected in wide pressure and temperature ranges. Reliable short-range pair distribution functions have been determined using advanced ab-initio calculations (GNXAS) taking into account the medium and long-range structure obtained by previous neutron and x-ray-scattering studies.

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PubMed1998

Two recent developments in XMCD.

This paper reports on two new technical developments concerning sample environments for X-ray magnetic circular dichroism (XMCD). The first measurements under high pressures of up to 30 GPa are described. The difficulties of combining the techniques of high pressure and XMCD are commented on. The second development involves the use of a fast-switching magnetic field. A new superconducting device is used to perform XMCD measurements on paramagnetic compounds in magnetic fields of up to 6 T. The small amplitude of the XMCD signal imposes, for a given signal-to-noise ratio, a noise less than a few 10(-5). The signal-to-noise ratio is improved by the use of a series of acquisitions, switching the magnetic field between each acquisition. A very fast switching mechanism has been built based on mechanical rotation of a superconducting coil, with the sample kept in place inside the coil. The XMCD signals at the L(II,III)-edges of paramagnetic rare-earth compounds have been measured at 4.5 K in fields of up to 6 T with a switching time of 11 s.

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