{Dy(α-fur)3}n: from double relaxation single-ion magnet behavior to 3D ordering

Abstract

The synthesis and magnetostructural properties of a new low-dimensional magnetic system based on α-furoate ligands, {[Dy(α-C₄H₃OCOO)(μ-(α-C₄H₃OCOO))₂(H₂O)₃]}_n, abbreviated {Dy(α-fur)₃}_n, are reported. X-ray diffraction experiments results evidence the presence of two different Dy coordination environment types differing only in the position of one of the furoate ligands. The crystallographic structure is formed by polymeric chains along the c-axis, each composed of just one Dy type, coupled within the bc-plane with chains of the same Dy type. These planes, each of them containing only one Dy type, are randomly stacked along the a-axis. The magnetic behaviour was studied by magnetization, static and dynamic susceptibility, heat capacity measurements and ab initio simulations. The directions of the easy axes of magnetization, gyromagnetic values and energy level structures of the two Dy types were obtained from ab initio calculations. {Dy(α-fur)₃}_n exhibits slow magnetic relaxation dynamics below 10 K. The two Dy types with different coordination environments behave as single-ion magnets, with different thermal activation energies of 80.5(6) K and 32.4(5) K, until they reach, upon cooling, a quantum tunneling (QT) regime. Magnetic diluted samples, substituting Dy by Y, {Y_xDy_1−x(α-fur)₃}_n, were prepared to study the effect of intercluster interactions. Decreasing the Dy interaction by dilution by 90–95% leaves the activation energy unchanged, but shifts the transition to the QT regime to lower temperatures. At T = 2.4 K the tunneling time constant has been shown to decrease weakly with the field in the x = 0 case, and more strongly for x = 0.9. As the external field increases, quantum tunneling is quenched and a new slow relaxation appears that is identified at high fields as caused by a direct relaxation process. As the temperature is decreased, interchain AF coupling becomes effective and gives rise to the occurrence of an antiferromagnetic 3D order transition at T_N = 0.66 K. From all the evidence, it is concluded that within each bc-plane Dy ions arrange in chains along the c-direction, having weak uncompensated ferromagnetic spin-canted intrachain coupling and antiferromagnetic interchain coupling.