Slow relaxation in a {Tb 2 Ba(α-fur) 8 } :N polymer with Ln = Tb(iii) non-Kramers ions
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BARTOLOME, Bartolome; ARAUZO, A.; LUZON, Javier; MELNYK, Silvia; SHOVA, Sergiu; PRODIUS, Denis; BARTOLOME, Juan; AMANN, Andreas; NALLAIYAN, Manivannan; SPAGNA, Stefano. Slow relaxation in a {Tb 2 Ba(α-fur) 8 } :N polymer with Ln = Tb(iii) non-Kramers ions. In: Dalton Transactions. 2019, nr. 15(48), pp. 5022-5034. ISSN 1477-9226.
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Dalton Transactions
Numărul 15(48) / 2019 / ISSN 1477-9226

Slow relaxation in a {Tb 2 Ba(α-fur) 8 } :N polymer with Ln = Tb(iii) non-Kramers ions


DOI: 10.1039/c8dt05044a
Pag. 5022-5034

Bartolome Bartolome1, Arauzo A.2, Luzon Javier23, Melnyk Silvia45, Shova Sergiu6, Prodius Denis54, Bartolome Juan2, Amann Andreas7, Nallaiyan Manivannan7, Spagna Stefano7
 
1 Escola Universitària Salesiana de Sarrià (EUSS), Barcelona,
2 Universidad de Zaragoza, Zaragoza,
3 Centro Universitario de la Defensa, Academia General Militar, Zaragoza,
4 Institute of Chemistry,
5 Academy of Sciences of Moldova,
6 “Petru Poni” Institute of Macromolecular Chemistry,
7 Quantum Design Inc.
 
Disponibil în IBN: 20 aprilie 2019


Rezumat

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 = C 4 H 3 OCOO ligands: {[Tb 2 Ba(α-fur) 8 (H 2 O) 4 ]·2H 2 O} n . The α-furoate ligands consolidate 1D zig-zag chains running along the c-axis, formed by Tb 2 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 and consists of a quasi-doublet with a Δ Tb /k B = 3.22 K gap, well separated from the next excited state, while the gap for the Tb 2 dimer is Δ 2Tb /k B = 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′∗/k B = -1.6 K. Dipolar interactions couple the Tb ions in the dimer with their first neighbour ions along the chain, with J′′∗/k B = -0.15 K, and with the surrounding ions out of the chain, with maximum J′′′∗/k B = -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/k B = 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 {[Dy 2 Ba(α-fur) 8 (H 2 O) 4 ]·2H 2 O} n , differing only in the Kramers nature of the ions, and the mononuclear {Ln(α-fur) 3 (H 2 O) 3 } n (Ln = Tb, Dy) complexes, previously reported.