High relaxation barrier in neodymium furoate-based field-induced SMMs. Issue 41 (1st July 2019)

• Record Type: Journal Article
• Authors: Bartolomé, E.; Arauzo, A.; Luzón, J.; Melnic, S.; Shova, S.; Prodius, D.; Nlebedim, I. C.; Bartolomé, F.; Bartolomé, J.
• Is Part Of: Dalton transactions. Volume 48:Issue 41(2019)
• Page Start: 15386
• Page End: 15396
• Publication Date: 2019-07-01
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c9dt02047k
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Two new neodymium molecular magnets of formula {[Nd(α-fur)3 (H2 O)2 ]·DMF} n (1 ) and {[Nd0.065 La0.935 (α-fur)3 (H2 O)2 ]} n (2 ), α-fur = C4 H3 OCOO, have been synthesized and characterized. Abstract : Two new neodymium molecular magnets of formula {[Nd(α-fur)3 (H2 O)2 ]·DMF} n (1 ) and {[Nd0.065 La0.935 (α-fur)3 (H2 O)2 ]} n (2 ), α-fur = C4 H3 OCOO, have been synthesized. In (1 ) the furoate ligands, in bidentate bridging mode, consolidate zig-zag chains running along the a -direction. Compound (2 ) is a magnetically diluted complex of a polymeric chain along the b -axis. Heat capacity, dc magnetization and ac susceptibility measurements have been performed from 1.8 K up to room temperature. Ab initio calculations yielded the gyromagnetic factors g x * = 0.52, g y * = 1.03, g z * = 4.41 for (1 ) and g x * = 1.35, g y * = 1.98, g z * = 3.88 for (2 ), and predicted energy gaps of Δ / k B = 125.5 K (1 ) and Δ / k B = 58.8 K (2 ). Heat capacity and magnetometry measurements agree with these predictions, and confirm the non-negligible transversal anisotropy of the Kramers doublet ground state. A weak intrachain antiferromagnetic interaction J ′/ k B = −3.15 × 10 −3 K was found for (1 ). No slow relaxation is observed at H = 0, attributed to the sizable transverse anisotropy component, and/or dipolar or exchange interactions enhancing the quantum tunnelling probability. Under an external applied field as small as 80 Oe, two slow relaxation processes appear: above 3 K the first relaxation mechanism is associated to a combination of Orbach process, with a sizeable activation energy U / k B = 121 K at 1.2 kOe for (1 ), Raman and direct processes; the second, slowest relaxation mechanism is associated to a direct process, affected by phonon-bottleneck effect. For complex (2 ) a smaller U / k B = 61 K at 1.2 kOe is found, together with larger g *-transversal terms, and the low-frequency process is quenched. The reported complexes represent rare polymeric Nd single-ion magnets exhibiting high activation energies among the scarce Nd(iii ) family.