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

Abstract

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]·CHCl3 (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 DyIII and CrIII 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 Δeff = 3 cm-1. Density-functional theory calculations show that the Dy-Cr couplings originate from superexchange via the fluoride bridges. © 2012 The Royal Society of Chemistry.

Publication Title

Chemical Science

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