Characterization of relaxed photo-excited magnetized states in prussian-blue analogous magnets

Local structure of a photo- or x-ray-induced ferrimagnet Cs_0.8Co_1.3 [W(CN)₈](3-cyanopyridine)_1.9(2.1H₂O was investigated by means of Co K- and W L-edge XAFS spectroscopy. The Co K-edge XANES spectra provide quantitative information on the ratio of Co(II) and Co(III) by virtue of the factor analysis. It was found that the Co(II) ratios are 81.9% at 300 K and 32.7% at 150 K. When the sample was irradiated by x rays at 30 K, a phase transformation occurred in a similar manner to the visible-light irradiation and a relaxed excited state that exhibits ferrimagnetism was formed. The relaxed excited state gives the Co(II) ratio of 67.0%. The W L_III-edge EXAFS spectra determine the W-C, W-N and W-Co distances. The results of the distances were obtained as R(W-C)=2.16 Å, R(W-N)=3.31 Å, R(W-Co^II)=5.37 Å and R(W-Co^III)=5.19 Å, irrespective of the three phases. The local structure of the relaxed excited state was found to be identical with that of the high-temperature (300 K) phase. The phase transformation is concluded to be caused by the charge transfer and the spin flipping from the -W^IV(S=0)-CN-Co^III (S=0)- configuration to -W^V(S=1/2)-CN-Co^II (S=3/2)-.