Investigation of K2MnF5 center dot H2O by neutron diffraction

Crystal and magnetic structures of the chain pentafluoromanganate K2MnF5. H 2O have been investigated by means of neutron powder diffraction, Neutron d ata recorded in the paramagnetic state are consistent with the monoclinic P 2(1)/m space group and have allowed us to confirm a previously proposed str uctural model with a < c. K2MnF5. H2O orders antiferromagnetically below T- N = 16.2 K (propagation vector k = (0 0 1/2)) and the magnetic structure ca n be described by antiferromagnetic chains coupled in a ferromagnetic manne r along a and antiferromagnetically along c, The magnetic moment of Mn3+ io ns is found to be equal to 3.1(1) mu(B) at 1.5 K. We have determined the co nditions to be satisfied by the isotropic exchange integrals in order to ob tain the observed magnetic structure as the ground state. (C) 2000 Academic Press.