Magnetic neutron diffraction study of the charge-ordered chain compounds Rb11Mn8O16and Cs3Mn2O4

Abstract

The magnetic ordering patterns of Rb${}_{11}$Mn${}_{8}$O${}_{16}$ and Cs${}_{3}$Mn${}_{2}$O${}_{4}$ were determined by neutron powder diffraction with and without applied magnetic fields. The crystal structures of these compounds exhibit infinite chains of edge-sharing MnO${}_{4}$ tetrahedra with periodically alternating Mn${}^{2+}$ and Mn${}^{3+}$ valence. Both Rb${}_{11}$Mn${}_{8}$O${}_{16}$ and Cs${}_{3}$Mn${}_{2}$O${}_{4}$ show collinear magnetic order with antiferromagnetic alignment of Mn moments along the chains below the N\'eel temperatures ${T}_{\mathrm{N}}$ $=$ 38(1) and 13.5(5) K, respectively. In Cs${}_{3}$Mn${}_{2}$O${}_{4}$ the Mn${}^{2+}$ and Mn${}^{3+}$ moments could be separately refined. The full magnetic structure in a zero magnetic field can be viewed as a set of ferrimagnetic chains whose net moments are coupled antiferromagnetically perpendicular to the chain direction. For this compound, we further observe a magnetic field induced transition into a high-field phase with uniformly aligned ferrimagnetic moments.