57Fe Mossbauer Spectroscopic Study on Fe2+-Oxides with Infinite-Layer and Ladder Structures

On the basis of Mossbauer spectroscopy, we studied the magnetic properties of a pair of square-planar coordinated Fe2+ (S = 2)-oxides, SrFeO2 (112) and Sr3Fe2O5 (325). The infinite layered structure for the 112 phase and the two-legged ladder structure for the 325 phase are suggestive of magnetic low dimensionality but, in fact, both these oxides have been found to have high Neel temperatures of T-N = 468 K (112) and 296 K (325). Significantly strong FeO4 face-to-FeO4 face interactions between the layers (112) and between the ladders (325) have thus been suggested. The intrinsic isomer shift, a Mossbauer spectroscopic parameter measuring the s electron density at the Fe-57 nucleus, was estimated to be so small as similar to 0.7 mm s(-1) for both 112 and 325, indicating the specificity of the square planer coordination.