Strong magnetic exchange and frustrated ferrimagnetic order in a weberite-type inorganic–organic hybrid fluoride

Abstract

We combine powder neutron diffraction, magnetometry and 57 Fe Mössbauer spectrometry to determine the nuclear and magnetic structures of a strongly interacting weberite-type inorganic–organic hybrid fluoride, Fe 2 F 5 (H taz ). In this structure, Fe 2+ and Fe 3+ cations form magnetically frustrated hexagonal tungsten bronze layers of corner-sharing octahedra. Our powder neutron diffraction data reveal that, unlike its purely inorganic fluoride weberite counterparts which adopt a centrosymmetric Imma structure, the room-temperature nuclear structure of Fe 2 F 5 (H taz ) is best described by a non-centrosymmetric Ima 2 model with refined lattice parameters a = 9.1467(2) Å, b = 9.4641(2) Å and c = 7.4829(2) Å. Magnetic susceptibility and magnetization measurements reveal that strong antiferromagnetic exchange interactions prevail in Fe 2 F 5 (H taz ) leading to a magnetic ordering transition at T N = 93 K. Analysis of low-temperature powder neutron diffraction data indicates that below T N , the Fe 2+ sublattice is ferromagnetic, with a moment of 4.1(1) µ B per Fe 2+ at 2 K, but that an antiferromagnetic component of 0.6(3) µ B cants the main ferromagnetic component of Fe 3+ , which aligns antiferromagnetically to the Fe 2+ sublattice. The zero-field and in-field Mössbauer spectra give clear evidence of an excess of high-spin Fe 3+ species within the structure and a non-collinear magnetic structure. This article is part of the theme issue ‘Mineralomimesis: natural and synthetic frameworks in science and technology’.

Investigation of the magnetic phase diagram of the 2D ferrimagnetic J 1–J 2 model

“…That does not mean that the investigation of ferrimagnets, in general, is not an active field. The contrary is the case [22][23][24][25][26][27][28][29]. In this publication, we use with the time-dependent cluster mean-field theory (t-CMFT) a quantum-mechanical method to describe the ferrimagnetic J 1 -J 2 model.…”

A Geometrically Frustrated Family of MIIMIIIF5(H2O)2 Mixed–Metal Fluorides with Complex Magnetic Interactions

“…Two additional important differences are the replacement of two F atoms by water molecules and the absence of A cations (Figure ). ,, Both weberites and inverse weberites have been investigated to understand the concept of coupled magnetic frustration in compositions where two types of cations occupy distinct crystallographic sites. ,,,, In the 1980s, Laligant et al successfully synthesized M II Fe III F 5 (H 2 O) 2 (M II = Fe, Mn, Co, Ni, Zn) using solvothermal methods and their studies indicated that in inverse weberites frustrated magnetism can be induced when both M II and M III have unpaired electrons. ,,,− However, frustrated magnetism properties were studied only for Fe 3+ -based compounds, and those of other inverse weberite structures have not yet been studied.…”

Introduction: minerals to metal-organic frameworks

“…My own group's contribution to the issue is an example of a phase transition under pressure, illustrating how host-guest hydrogen bonding-a unique feature in coordination frameworks compared to their mineral analogues-can stabilize particular crystallographic structures [25]. The articles from the groups of Clark [26] and of Saines [27] both consider magnetic frustration in different framework topologies. Magnetic exchange is among the subtlest and most variable features of coordination frameworks, and these articles demonstrate the variety of magnetic order and disorder that can be achieved even in apparently analogous materials.…”