A Mössbauer spectroscopy investigation of the Intergrowth Phases LaSr3Fe3−xMx010−δ (M = Al,Cu)

Iron-57 Mössbauer spectroscopy confirms a high sensitivity of the three-dimensional magnetic ordering temperature (T_Néel) for a series of new intergrowth phases to both oxygen stoichiometry and the partial substitution of iron by copper and aluminium in the Ruddlesden-Popper phase LaSr₃Fe₃0_10?δ. The chemical isomer shifts suggest that significant covalent electron delocalization exists in these phases. Spectra for the paramagnetic phases indicate two distinct iron coordination environments consistent with x-ray and neutron diffraction structure determinations. The Mössbauer spectra at 4.8 K exhibit the overlap of two magnetic hyperfine patterns corresponding to cooperative magnetic order at the iron sites with internal fields of 45 and 27 Tesla for nominal Fe³⁺ and Fe⁴⁺ sites respectively.