Structural and magnetic properties of the low-dimensional fluoride β-FeF3(H2O)2·H2O

Abstract

We have reinvestigated the crystal structure of the low-dimensional fluoride β-FeF₃(H₂O)₂·H₂O using high resolution neutron and X-ray diffraction data. Moreover we have studied the magnetic behavior of this material combining medium resolution and high flux neutron powder diffraction together with magnetic susceptibility measurements. This fluoride compound exhibits vertex-shared 1D Fe³⁺ octahedral chains, which are extended along the c-axis. The magnetic interactions between adjacent chains involve super-superexchange interactions via an extensive network of hydrogen bonds. This interchain hydrogen bonding scheme is sufficiently strong to induce a long range magnetic order appearing below T = 20(1) K. The magnetic order is characterized by the propagation vector k = (0, 0, 1/2), giving rise to a strictly antiferromagnetic structure where the Fe³⁺ spins are lying within the ab-plane. Magnetic exchange couplings extracted from magnetization measurements are found to be J_∥/k_b = −18 K and J_⊥/k_b = −3 K. These values are in good agreement with the neutron diffraction data, which show that the system became antiferromagnetically ordered at ca. T_N = 20(1) K.