In this work, we observed a spin-crossover phenomenon in a cesium iron hexacyanochromate, which is a Prussian blue analogue. This compound showed a thermal phase transition with transition temperatures of 211 K (T1/2 downward arrow) and 238 K (T1/2 upward arrow) due to a spin-crossover on FeII sites. This spin-crossover phase transition is accompanied by a lattice contraction of 0.38 A, but maintains a face-centered cubic structure (F3m). This is the first observation of FeII spin-crossover in a series of Prussian blue analogues.

We report unusual observations in the magnetic behavior of Sn 1−x 57 Fe x O 2−␦ powders prepared by a sol-gel method. Mössbauer spectra showed three different sites for those irons in the SnO 2 lattice. The samples seem to exhibit many sources of ferromagnetism, and the dominance of one of them greatly depends upon the synthesis conditions. In one sample, prepared using citric acid solution of metal Fe and annealed at 500°C for two hours, we observed magnetization, but its room temperature Mössbauer spectrum did not show any magnetic component, suggesting that the ferromagnetism could not have originated from the iron ions but from magnetic defects. In another sample prepared from chloride acid solution of Fe 2 O 3 and annealed at 600°C for six hours, a large magnetization and a sextet with broad lines were observed and the ferromagnetism was ascribed to iron impurities. In another sample prepared from citric acid solution of metal Fe but annealed at 650°C for two hours, we observed an intensive magnetic sextet with sharp lines but small magnetization, suggesting the presence of hematite doped with tin.

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