M ssbauer spectroscopy under a magnetic field to explore the low-temperature spin structure of the layered ferrimagnetic material— N(n-C4H9)4[FeIIFeIII(C2O4)3]

57Fe Mossbauer spectroscopy of the metal-assembled layered ferrimagnetic material {N(n-C4H9)4[FeIIFeIII(C 2O4)3]}∞ was performed under a high external magnetic field at 4.2 K. This study successfully detected different types of FeII and FeIII high spin sites in the lattices. The hyperfine field values estimated for all the FeIII high spin sites are close to the expected values, whereas those for FeII high spin sites are substantially different to those expected usually. A large fraction of magnetically disordered FeIII high spin sites were found. It is understood that the layered structure of the compound may have two kinds of sub-lattices—(FeAII–ox–Fe AIII–···) and (FeBII–ox–Fe BIII–···)—along with randomly placed magnetically disordered FeCIII sites, where the FeAIII and FeBIII are antiferromagnetically aligned. The existence of the magnetically and/or structurally non-equivalent spin sites in the same lattice has been held responsible for the coexistence of different ferrimagnetic interactions leading to the spin glass state, as observed through earlier magnetic and calorimetric measurements.