Low-temperature magnetism of Ln2Ba (Ln = Nd, Er, Ho) furoate-based polymeric chains: Slow relaxation, magnetic anisotropy and interactions

Abstract

The synthesis, structure and magnetothermal properties of three new lanthanide 1D polymeric complexes, {[Ln2Ba(α-fur)8(H2O)4]}n for Ln = Nd (1), Er (2) and {[Ho2Ba(α-fur)8(H2O)4]⋅2H2O}n (3), based on carboxylic α-fur = C4H3OCOO ligands is reported. The α-furoate ligands consolidate zigzag chains formed by Ln2 dimers separated by Ba ions. Ab initio calculations, in combination with the fit of experimental static magnetization and heat capacity, predict the magnetic ground state, energy levels and magnetic interactions in these heteronuclear nanomagnets. Nd2Ba (1) presents two different coordination sites for Nd, with an orthorhombic magnetic ground state. Nd ions are coupled along the chain through a weak antiferromagnetic (AF) interaction J″/kB = −0.08 K. Er(III) ions in Er2Ba (2) present a highly axial ground state, forming magnetic dimers with an interaction of J′/kB = −8.6 K, while interdimer coupling along the chain is J″/kB = −0.28 K. The Ho2Ba (3) complex consists of a highly anisotropic quasi-doublet with a ΔHo/kB = 0.7 K gap. Non-Kramers Ho ions form magnetic dimers within the Ho2Ba cluster, coupled by an AF intradimer interaction J′/kB = −2.5 K. The three complexes exhibit in-field slow relaxation of the magnetization: 1 relaxes through an Orbach process at high temperatures [Ueff/kB = 60(1) K] evolving to quantum tunneling below 3 K [τQT = 0.05(1) s]; 2 exhibits a rapid Orbach-like process [τ0 = 8(6)⋅10–8 s and Ueff/kB = 10(2) K] and 3 shows a direct process [τ = 0.4(1) s].