Structural characterization of the Co/Cr multilayers by x-ray-absorption spectroscopy

We have performed Cr and Co K-edge x-ray-absorption measurements to investigate the dependence of local electronic and atomic structures on the Cr-layer thickness in epitaxial Co(11̄00) (40 Å)/Cr(211) (t_Cr) (t_Cr = 2, 3, 5, 7, and 9 Å) multilayers. The Cr K x-ray-absorption near-edge fine structure (XANES) spectra of the Co/Cr multilayers indicate an abrupt transition of the Cr layer from hcp to bcc structure when the thickness of the Cr layer is increased to exceed ∼5 Å or three atomic layers. Our results offer an upper limit for the ability of the Co/Cr interface to stabilize the hcp structure in the thin Cr layer. The numbers of nearest-neighbor and next-nearest-neighbor atoms in the Cr and Co layers determined by extended x-ray-absorption fine-structure measurements performed at the Cr and Co K edge, respectively, are consistent with the XANES results.