A Series of Chiral, Polar, Homospin Topological Ferrimagnets: M₃(OOCH)₅Cl(OH₂) (M = Fe, Co, Ni)

Abstract

An isostructural series of transition metalformate-chloride-hydrate compounds, M 3 (OOCH) 5 Cl(OH 2 ) (M = Fe, Co, Ni), have been synthesized using a solvothermal method. These compounds crystallize in the chiral and polar space group P3 1 and are comprised of three different types of helical chains of edge-sharing M 2+ -centered octahedra. All three compounds undergo 3D ferrimagnetic ordering at low temperature, and the iron and cobalt analogues exhibit fieldinduced metamagnetic transitions. The magnetic structure was determined by neutron powder diffraction, revealing ferromagnetic intrachain coupling and antiferromagnetic interchain interactions, with the three chains arranged in a two-up/onedown triangular lattice. As all three chains contain one type of metal in the same spin state, these compounds are rare examples of homospin topological ferrimagnets.

Neutron Instruments for Research in Coordination Chemistry

“…In terms of coordination chemistry, HB‐2A has been utilized primarily to access the magnetic structures of the compounds . Hydrogen atom is a strong incoherent scatter for neutrons and therefore adds a large background to measurements of hydrogen‐continuing compounds, which has to be considered when dealing with often small signals from magnetic scattering.…”

“…Neutron powder diffraction and magnetic structure of Co 3 (OOCH) 5 Cl(OH 2 ) measured on HB‐2A. [110a] (A) Diffraction patterns taken at 10 K and 1.5 K show additional magnetic reflections at 1.5 K. Inset: Order parameter for the (1,0, 1,0) reflection, compared to the temperature dependence of the magnetic susceptibility. (B) Rietveld refinement of the 1.5 K data.…”

“…However, a notable counter example using polarized neutron diffraction can be found in the study of the Prussian blue analog coordination polymer. [110c] Polarizing the incident beam and then controlling the direction of an applied field allows highly sensitive access to ferromagnetic and ferrimagnetic ordering . Extra counting times are often required since producing the polarized beam necessarily reduces the flux.…”

“…Designs through coordination chemistry have led to low‐dimensional magnetic systems by suitable control of the 3D crystal structure to include well isolated one‐dimensional (1D) chains or two‐dimensional (2D) layers. [110a] The further introduction and control of high magnetic anisotropy or multiferroicity, for example, can then lead to potentially useful applied physical properties. A series of such chiral, polar topological ferrimagnets have been investigated on HB‐2A (Figure ).…”

“…These compounds M 3 (OOCH) 5 Cl(OH 2 ) [M = Fe II , Co II , Ni II ] are composed of 1D chains that are twisted into helices. [110a] The magnetic structure was determined using variable‐temperature (VT) neutron powder diffraction on HB‐2A, indicating that the moments are aligned in the same direction as the polarity of the helical chains. The results suggest that these materials could be potential multiferroics.…”