CHARACTERIZATION OF MAGNETIC COFE CYANIDES BY X-RAY-ABSORPTION FINE-STRUCTURE SPECTROSCOPY

X-ray-absorption fine-structure spectra were measured and analyzed for several FeCo cyanides MxCoyFe(CN)(6). zH(2)O (M = Na, K, Rb) which ar e known to exhibit interesting magnetic properties depending on temper ature. X-ray-absorption near-edge structure spectra allow us to confir m very clearly the spin transitions in Na0.4Co1.3Fe(CN)(6). 5H(2)O and K0.4Co1.3Fe(CN)(6). 5H(2)O and to evaluate the composition ratios of Co-II and Co-III species quantitatively. The Co-II:Co-III ratios are e ssentially important physical quantities with which to understand magn etic properties. The local structures around Fe and Co atoms were dete rmined by the Fe and Co K-edge extended x-ray-absorption fine-structur e spectra. It is confirmed that the local structures around Fe are Fe( CN)(6)Co-6 (the subscripts denote the coordination numbers) while thos e around Co are Co(NC)(6-1/y)(H2O)(1/y)Fe6-1/y. The first-nearest-neig hbor Fe-C distances do not significantly change between Fe-II and Fe-I II species, while the first-nearest-neighbor Go-NO distances are notic eably different between Co-II and Co-III ones. The difference of as mu ch as 0.16-0.20 Angstrom between Co-II and Co-III, which corresponds w ell to that for typical Co tautomeric complexes, causes noticeable cha nge of the lattice constant.