Jeudi 26 Juin 2008 à 14h30

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Jeudi 26 Juin 2008 à 14h30, vous êtes convies en salle 105 (au 1er étage du bâtiment des amphis de l'INSA).
Nicolas Jaouen (Synchrotron SOLEIL) présentera le séminaire suivant :
"Magnetism in low dimensional system probe by X-ray magnetic circular dichroism and X-ray resonant magnetic scattering"

Many current forthcoming applications of magnetic materials involve heterostructures or alloys containing magnetic and non-magnetic elements. However, to design novel magnetic materials with specific magnetic characteristics, the knowledge of the spin-polarization and exchange-coupling mechanisms in such materials is mandatory. X-ray magnetic circular dichroism (XMCD) and its scattering counterpart (X-ray Resonant Magnetic Reflectivity or XRMR) are the technique of choice to probe such phenomena thanks to their element-selectivity (and spatial sensitivity). We will show that a wealth of information regarding the microscopic origin of magnetism in low dimensional magnetic systems can be extracted from XMCD and XRMS.

Therefore, this talk reviews recent results in XRMS experiments. In the first part of this talk the principle of XMCD and XRMS and the main strengths of this element selective technique will be presented and illustrated through concrete examples. The experimental aspects of XMCD and XRMS will be introduced. In particular the experimental the set-up planned to be in operation at SOLEIL in 2010 (Deimos and Microfocus

Beamline) will be presented.

The first example will be with a special focus on induced magnetism in “non-magnetic” layers. In particular, I will present the capability of XRMS associated with XMCD to give experimental information on the effective exchange interaction between two ferromagnetic layers across a non-magnetic (4d or 5d) spacer. To get more insight on the mechanism governing this exchange interaction, the experimental results will be compared with recent band structure calculations. Then in a second part, I will reports the recent results obtained thanks to X-ray absorption

(XAS) and magnetic circular dichroism (XMCD) spectroscopy of as-deposited and postannealed Fe50Pt50/C granular multilayers. The XAS and XMCD were measured at both the Fe and Pt L_2,3 edges allowing to extracted separately the spin and orbital moment of both elements and we demonstrate that thermal annealing at temperatures above 600°C results in the growth of the FePt nanoparticles by coalescence and their gradual L10 ordering, which induces magnetic hardening. X-ray resonant scattering has been used and we will show that it can be used to extract more information regarding the magnetic structure of these nanoparticles.

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