Magnetic structure and dynamics of a strongly one-dimensionalcobaltIImetal-organic framework

Abstract

We investigate the magnetism of the Co II 4(OH)2(C10H16O4)3 metal-organic framework which displays complex inorganic chains separated from each other by distances of 1 to 2 nm, and which orders at 5.4 K. The zero-field magnetic structure is determined using neutron powder diffraction: it is mainly antiferromagnetic but posseses a ferromagnetic component along the c-axis. This magnetic structure persists in presence of a magnetic field. Ac susceptibility measurements confirm the existence of a single thermally activated regime over 7 decades in frequency (E/kB ≈ 64 K) whereas time-dependent relaxation of the magnetization after saturation in an external field leads to a two times smaller energy barrier. These experiments probe the slow dynamics of domain walls within the chains: we propose that the ac measurements are sensitive to the motion of existing domain walls within the chains, while the magnetization measurements are governed by the creation of domain walls.

Probing magnetic interactions in metal–organic frameworks and coordination polymers microscopically

“…11). 84 The moments of the octahedral cations lie close to the equatorial plane while those of the trigonal bipyramids are canted further out of their equatorial plane, as commonly observed for strong anisotropy in this coordination environment. Nearestneighbour octahedral cations are antiferromagnetically coupled to each other while the square pyramidal Co cations are ferromagnetically coupled to the octahedral Co cations with which they share an edge.…”

“…Neutron powder diffraction measurements were obtained from a hydrogenated sample (51 atom % H) of Co 4 (OH) 2 (seb) 3 and the magnetic structure analysed from temperaturesubtracted data. 84 All magnetic reflections were indexed on a structure with a k-vector of 0 and representation analysis was used to determine the possible magnetic structures. The magnetic structure was determined to have octahedral Co cation spins aligned parallel to the chain while those of the Co in the trigonal bipyramids are tilted from the chain axis by 35° resulting in a non-collinear structure (see Fig.…”

“…The net magnetisation per Co cation in the magnetic structure of Co 4 (OH) 2 (seb) 3 is 0.82 µ B , which is consistent with the magnetisation jump observed at very low applied fields being caused by this net magnetisation being aligned with the magnetic field. 83,84 Neutron diffraction patterns were also collected in an applied field, with the sample immersed in deuterated isopropanol, which freezes at low temperature to form a glass to fix the grains of sample in place. 84 The patterns did not show any obvious sign of a magnetic phase transition up to 2 T but relative temperature intensities of the reflections relevant to the spin canting in the chains suggestive of significant rearrangements of the spins were noted but the restricted data quality prevented detailed analysis.…”

“…83,84 Neutron diffraction patterns were also collected in an applied field, with the sample immersed in deuterated isopropanol, which freezes at low temperature to form a glass to fix the grains of sample in place. 84 The patterns did not show any obvious sign of a magnetic phase transition up to 2 T but relative temperature intensities of the reflections relevant to the spin canting in the chains suggestive of significant rearrangements of the spins were noted but the restricted data quality prevented detailed analysis. Diffuse magnetic scattering was seen in 0.5 and 2 T fields up to 10 and 13 K, indicative of the persistence of interchain correlations well above the Néel temperature.…”

“…Almost all of these highhydrogen content samples have had their magnetic structures analysed using high flux instruments at reactor sources, avoiding concerns with multi-wavelength dependant attenuation corrections at time-of-flight based instruments. 38,40,57,75,84,116 This emphasises the importance of both continued access to reactor-based neutrons and more robust data correction from modern spallation sources.…”