Search

The results of a systematic study of Magnetic EXAFS at K edges of transition metals (TM) and L edges of rare earth (RE) compounds are presented. At the K edges of TM the magnetic EXAFS is in phase with the normal EXAFS in all studied cases and its intensity is related to the variation of the mean magnetization. At L edges, magnetic EXAFS is not correlated with the complex magnetic dichroism observed at the edge. By studying the phase difference between the magnetic and normal EXAFS, we observe that there exists an interplay between the contribution of the central atom (giving a contribution to the phase in quadrature with normal EXAFS) and the magnetic neighbours (giving a contibution in phase). Multiple excitations are frequently observed in the spectra with a greater sensitivity than in normal EXAFS.

To explain the low-energy features of magnetic circular X-ray dichroism (MCXD) at L edges of rare earth compounds, quadrupolar electric transitions (E2) from 2p to 4f levels have been invoked. Such transitions should be distinguished from dipolar electric (E1) ones by looking at the different behaviour of the E1 and E2 MCXD cross sections as a function of the temperature and the angle the quantization axis and the photon wave vector. However, convincing experimental proof of such transitions has not yet been given. A good candidate for these key tests is Yb, where the E2 transitions are allowed at the L2 edge and forbidden at the L2 edge. In YbFe2, we observe an important change in the shape of the spectrum with temperature with temperature at the L3 edge of Yb.