Effect of 3d-4f Magnetic Exchange Interactions on the Dynamics of the Magnetization of Dy lll-M ll- Dy lll Trinuclear Clusters
Résumé
[{Dy(hfac)3}2{Fe(bpca)2}]CHCl3 ([Dy2Fe]) and [{Dy(hfac)3}2{Ni-(bpca)2}]*CHCl3 ([Dy2Ni]) (in which hfac=1,1,1,5,5,5-hexafluoroacetylacetonate and bpca=bis(2-pyridylcarbonyl) amine anion) were synthesized and characterized. Single-crystal X-ray diffraction shows that [Dy2Fe] and [Dy2Ni] are linear trinuclear complexes. Static magnetic susceptibility measurements reveal a weakferroma gnetic exchange interaction between NiII and DyIII ions in [Dy2Ni], whereas the use of the diamagnetic FeII ion leads to the absence of magnetic exchange interaction in [Dy2Fe]. Dynamic susceptibility measurements show a thermally activated behavior with the energy barrier of 9.7 and 4.9 K for the [Dy2Fe] and [Dy2Ni] complexes, respectively. A surprising negative effect of the ferromagnetic exchange interaction has been found and has been attributed to the structural conformation of these trinuclear complexes.