Direct observation of a ferri-to-ferromagnetic transition in a fluoride-bridged 3d-4f molecular cluster

Dreiser, Jan; Pedersen, Kasper S.; Piamonteze, Cinthia; Rusponi, Stefano; Salman, Zaher; Ali, Md. Ehesan; Schau-Magnussen, Magnus; Thuesen, Christian Aa.; Piligkos, Stergios; Weihe, Høgni; Mutka, Hannu; Waldmann, Oliver; Oppeneer, Peter; Bendix, Jesper; Nolting, Frithjof; Brune, Harald

doi:10.1039/c2sc00794k

Direct observation of a ferri-to-ferromagnetic transition in a fluoride-bridged 3d-4f molecular cluster

Dreiser J, Pedersen KS, Piamonteze C, Rusponi S, Salman Z, Ali ME, Schau-Magnussen M, Thuesen CA, Piligkos S, Weihe H, Mutka H, Waldmann O, Oppeneer P, Bendix J, Nolting F & Brune H

Citation

Dreiser, J., Pedersen, K. S., Piamonteze, C., Rusponi, S., Salman, Z., Ali, M. E., … Brune, H. (2012). Direct observation of a ferri-to-ferromagnetic transition in a fluoride-bridged 3d-4f molecular cluster. Chemical Science, 3(4), 1024-1032. https://doi.org/10.1039/c2sc00794k

Persistent URL https://www.dora.lib4ri.ch/psi/islandora/object/psi:12485

We report on the synthesis, crystal structure and magnetic characterisation of the trinuclear, fluoride-bridged, molecular nanomagnet [Dy(hfac)₃(H₂O)-CrF₂(py)₄-Dy(hfac)₃(NO₃)] (1) (hfacH = 1,1,1,5,5,5-hexafluoroacetylacetone, py = pyridine) and a closely related dinuclear species [Dy(hfac) ₄-CrF₂(py)₄]·½CHCl₃ (2). Element-specific magnetisation curves obtained on 1 by X-ray magnetic circular dichroism (XMCD) allow us to directly observe the field-induced transition from a ferrimagnetic to a ferromagnetic arrangement of the Dy and Cr magnetic moments. By fitting a spin-Hamiltonian model to the XMCD data we extract a weak antiferromagnetic exchange coupling of j = -0.18 cm^-1 between the Dy^III and Cr^III ions. The value found from XMCD is consistent with SQUID magnetometry and inelastic neutron scattering measurements. Furthermore, alternating current susceptibility and muon-spin relaxation measurements reveal that 1 shows thermally activated relaxation of magnetisation with a small effective barrier for magnetisation reversal of Δ_eff = 3 cm^-1. Density-functional theory calculations show that the Dy-Cr couplings originate from superexchange via the fluoride bridges.