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Issue 15, 2019
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Slow relaxation in a {Tb2Ba(α-fur)8}n polymer with Ln = Tb(iii) non-Kramers ions

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Abstract

We report the synthesis, crystal structure and magnetic properties of a new heteronuclear polymeric complex based on non-Kramers Tb ions and carboxylic α-fur = C4H3OCOO ligands: {[Tb2Ba(α-fur)8(H2O)4]·2H2O}n. The α-furoate ligands consolidate 1D zig-zag chains running along the c-axis, formed by Tb2 dimers separated by Ba ions. Ab initio calculations, in combination with the fit of experimental data, predict that the single-ion magnetic ground state is highly anisotropic (Image ID:c8dt05044a-t1.gif) and consists of a quasi-doublet with a ΔTb/kB = 3.22 K gap, well separated from the next excited state, while the gap for the Tb2 dimer is Δ2Tb/kB = 2.58 K. Static magnetization and heat capacity measurements show that, magnetically, the system can be modeled as dimers of non-Kramers Tb ions, coupled by an antiferromagnetic intradimer interaction J′*/kB = −1.6 K. Dipolar interactions couple the Tb ions in the dimer with their first neighbour ions along the chain, with J′′*/kB = −0.15 K, and with the surrounding ions out of the chain, with maximum J′′′*/kB = −0.03 K. Ac susceptibility measurements in H = 0 performed down to 50 mK temperatures have enabled us to observe slow relaxation of magnetization, with an Orbach-like activation energy of U/kB = 1.1 K. It is assigned to the sluggish response of the 3D spin system due to a short-range ordering, possibly enhanced by the presence of disorder caused by defects in the polymeric chains. Under the application of a magnetic field, the system slowly relaxes by two distinct direct processes, strongly affected by a phonon bottleneck effect. We discuss the different relaxational phenomenology of the new complex in comparison with that of the isostructural {[Dy2Ba(α-fur)8(H2O)4]·2H2O}n, differing only in the Kramers nature of the ions, and the mononuclear {Ln(α-fur)3(H2O)3}n (Ln = Tb, Dy) complexes, previously reported.

Graphical abstract: Slow relaxation in a {Tb2Ba(α-fur)8}n polymer with Ln = Tb(iii) non-Kramers ions

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Article information


Submitted
21 Dec 2018
Accepted
08 Mar 2019
First published
20 Mar 2019

Dalton Trans., 2019,48, 5022-5034
Article type
Paper

Slow relaxation in a {Tb2Ba(α-fur)8}n polymer with Ln = Tb(III) non-Kramers ions

E. Bartolomé, A. Arauzo, J. Luzón, S. Melnic, S. Shova, D. Prodius, J. Bartolomé, A. Amann, M. Nallaiyan and S. Spagna, Dalton Trans., 2019, 48, 5022
DOI: 10.1039/C8DT05044A

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