Spin-dependent extended x-ray absorption fine structure in magnetic oxides

The spin-dependent extended x-ray absorption fine-structure (EXAFS), i.e., the magnetic counterpart to the conventional EXAFS when using circularly polarized light in a ferro(i)magnet, was measured at the L_2,3 edges of Eu in Eu₃Fe₅O₁₂ and EuO and at the K edge of CrO₂. Complementary near-edge x-ray magnetic circular dichroism measurements at the O K edge were made to directly access the oxygen magnetization. It is shown that there is an influence of the nearly nonmagnetic oxygen atoms on the magnetic EXAFS depending on the local symmetry of the crystal as well as on the relative direction of the magnetic moments of neighboring atoms. The observed influences at distances corresponding to the oxygen neighbors in EuO are interpreted as the harmonic focusing effect, i.e., over-next magnetic neighbors behind the oxygen are responsible for the observed contributions.