A cerium M-edge X-ray absorption and an iron L-edge magnetic circular dichroism study of the Ce2Fe17-xMx solid solutions, where M is Al and Si

The cerium M-edge X-ray absorption spectra and the iron L-edge magnetic cir cular dichroism spectra of the Ce2Fe17-xMx solid solutions, where M is alum inum and silicon, were measured at room temperature. The cerium M-edge spec tra was used to determine the variation in the valence of cerium in the sol id solutions. The resulting values, which range from 3.20 in Ce2Fe16.8Si0.2 to 3.02 in Ce2Fe6Al11, decrease linearly with x in both series, but the de crease is twice as large in Ce2Fe17-xSix. Interestingly, the resulting vale ncies are quantitatively different from those determined using cerium L-edg e X-ray absorption data, but the qualitative trends in the valence with met alloid substitution is the same using either the cerium L- or M-edge data. The cerium valencies also correlate linearly with the cerium Wigner-Seitz c ell volumes, but with a positive slope for the silicon and a negative slope for the aluminum solid solutions. This difference results because of the m ore extensive cerium-silicon covalent bonding interaction in Ce2Fe17-xSix a s compared to the cerium-aluminum interaction in Ce2Fe17-xAlx. The iron L-e dge magnetic circular dichroism spectra indicate that a non-zero iron orbit al moment is coupled parallel to the iron spin moment. The orbital moments range from 0.0 to 0.2 mu(B) and reveal that the orbital moments are probabl y independent of x and are ca. 0.07 mu(B) for both series of solid solution s. The cerium M-edge magnetic circular dichroism spectra reveal no dependen ce upon the relative orientation of the magnetization or the photon helicit y, indicating that there is no 4f magnetic moment associated with cerium in these solid solutions. (C) 1999 Elsevier Science Ltd. All rights reserved.