Magnetic and Electronic Properties of Valence-Controlled Ni-Fe Cyanide

Magnetics and electronic properties has been investigated for the Prussian blue type cyano-bridged transition metal compound, Na0.72-delta Ni[Fe(CN)(6)](0.68)center dot 5.1H(2)O (0.0 <= delta <= 0.58), as a function of the hole concentration delta of the d-electron system. Mother compound (delta = 0) takes Ni2+ (t(2g)(6)e(g)(2): S = 1)-Fe2+ (t(2g)(6): S = 0) configuration, and is paramagnetic down to zero temperature. Holes are selectively introduced on the Fe site. Ferromagnetic transition appears at delta = 0.26, and the transition temperature T-C increases from 11 K at delta = 0.26 to 21 K at delta = 0.58. We further systematically investigated the absorption spectra in the infrared-violet region against delta. We compared these magnetic and electronic properties of the valence-controlled Ni-Fe compound with those of an isostructural valence-controlled Co-Fe compound.