L. Bozukov

Intermediate valence state of Ce in Ce2Fe14BHx

Abstract We present a combined X-ray absorption spectroscopy (XAS) and X-ray circular magnetic dichroism (XCMD) investigation performed at the Ce L-edges in the case of Ce 2 Fe 14 B and its hydride derivatives. Neither XAS nor XCMD data show any modification of the mixed-valence electronic state of cerium upon hydriding, indicating the absence of localized 4f magnetic moments in these systems.

Raman study of the 1222 compound (Bi,Cu)Sr2(R,Ce)2Cu2O9−δ (R=Y,Ho)

Abstract Ceramics of nominal composition (Bi 0.5 Cu 0.5 )Sr 2 (R 0.5 Ce 0.5 ) 2 Cu 2 O X (R = Y,Ho) were synthesized and characterized using XRD and SEM-EDX. The SEM-EDX analysis gives evidence for a large amount of (Bi,Cu1) vacancies, their number being dependent on the temperature of synthesis. From the polarized micro-Raman spectra all five A 1 g and two B 1 g Raman modes expected for 1222 compounds were identified at 126–131, 167–169, 236–256, 465–469, and 573–583 cm −1 , and at 163–164 and 298–304 cm −1 , respectively. The Raman lines were assigned to definite atomic vibrations in close comparison with other compounds of similar structure. The frequencies of the B 1 g -pair are explained by mixing of vibrations of oxygens in the Cu2O and (R,Ce)-O layers. The effect of (Bi,Cu1) vacancies on some Raman frequencies and a possible multimode behaviour of the (R,Ce)- A 1 g line are also discussed.

XAS Investigation of the Structural and Electronic Changes Induced by Hydrogen Absorption in CeFe11Ti

We present an extensive study using X-ray absorption spectroscopy on CeFe11 TiHx at variable hydrogen concentration. Cerium L3-edge, iron and titanium K-edge EXAFS and XANES spectra have been measured. We have investigated the influence of hydrogen absorption in electronic localization and local structure around the metal atoms as well as on the electronic state of cerium. The structural and magnetic changes in the hydrides are discussed in terms of the modification of the 4f-3d coupling strength via 3d-5d hybridization.

Mixed valence behavior in superconducting La1 − xCexRu2 compounds

We have used X-ray absorption spectroscopy (XAS) to investigate the role played by cerium into driving the superconductor behavior in the La 1-x Ce x Ru 2 solid solution. Trying to correlate the electronic changes detected by XAS with the magnetic and superconducting properties of these systems, we have also investigated the anomalous behavior of the low temperature transport properties of this series by measuring the resistivity down to 1.1 K, the magnetoresistance [0 < H < 2 T] and the heat capacity down to 4.7 K. These results are discussed in terms of the possible itinerant character of the Ce 4f electrons.

XAS investigation of the relationship between hydrogen uptake and Mn magnetic moment instability in RMn compounds

Abstract We report the results of X-ray absorption spectroscopy (XAS) investigation on the YMn 2 Hn x and GdMn 2 H x series aimed to obtain a deeper insight about the mechanism governing the modification of the magnetic behavior of both YMn 2 and GdMn 2 upon hydrogen absorption. Our results point out the role of the additional electrons injected in the system as hydrogen acts as an electron donor into the modification of the peculiar DOS of the RMn 2 systems.

ON THE DEVELOPING OF NET CE MAGNETIC MOMENT UPON H2 ABSORPTION IN CE2FE14B: AN XCMD INVESTIGATION

Abstract We present a combined X-ray Absorption Spectroscopy (XAS) and X-Ray Circular Magnetic Dichroism (XCMD) investigation performed at the Ce L-edges in the case of Ce2Fe14B and its hydride derivatives. Both XAS and XCMD data do not show any modification of the mixed-valence electronic state of cerium upon hydriding. In fact, our results rule out the hypothesis of the presence of a pure Ce3+ configuration in the hydride derivative and the resulting induction of a localized 4f magnetic moment on the Ce sites upon hydriding.