Spin Reorientation Associated with a Structural Transition in the Iron Oxycarbonate Sr4Fe2O6CO3

The oxycarbonate Sr4Fe2O6CO3 has been revisited, using a new synthesis route. Its microstructure has been established by electron microscopy and evidences an orthorhombic-monoclinic distortion at 220 K. The latter is associated with a spin reorientation (7) visible in magnetic susceptibility, heat capacity, and neutron diffraction studies. To understand the structural transition, particular attention has been paid for the carbonate groups: they adopt a specific orientation within a layer but different in successive layers, which involve disorder along and order in the (a,b) plane and are at the origin of the unusual broadening of the Mossbauer lines.