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

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On the basis of Mössbauer 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 Néel temperatures of $T_{\text{N}} = 468$ 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 Mössbauer spectroscopic parameter measuring the $s$ electron density at the 57Fe nucleus, was estimated to be so small as ${\sim}0.7$ mm s-1 for both 112 and 325, indicating the specificity of the square planer coordination.
2010-12-15