A neutron diffraction study of structural and magnetic transformations in AFeO(2) (A = K, Rb and Cs).

In continuation of our recent x-ray study of the structural phase transitions in the AFeO(2) (A = K, Rb, Cs) family, we have systematically investigated the respective structural and magnetic phase transitions by neutron powder diffraction. While the temperatures of the first-order structural phase transitions are strongly different for the three compounds (~1003, ~737 and ~350 K for A = K, Rb, Cs) and systematically decrease with increasing ionic radius of the A-cation, the magnetic transition temperatures in all three compounds have been found to be almost the same-slightly above 1000 K. The magnetic ordering type is similar in all three compounds-antiferromagnetic ordering of magnetic Fe(3 + ) ions within the system of the three-dimensional Fe-O-Fe linkages such that the Fe-Fe exchange between the nearest neighboring ions is always antiferromagnetic. The directions of magnetic Fe moments were found to be parallel to the crystallographic axis c in RbFeO(2) and CsFeO(2) and parallel to the axis b in KFeO(2) in notations of their low-temperature orthorhombic modifications.