Spin canting in a Dy-based single-chain magnet with dominant next-nearest-neighbor antiferromagnetic interactions

Abstract

We investigate theoretically and experimentally the static magnetic properties of single crystals of the molecular-based single-chain magnet of formula ${[\text{Dy}{(\text{hfac})}_{3}\text{NIT}({\text{C}}_{6}{\text{H}}_{4}\text{OPh})]}_{\ensuremath{\infty}}$ comprising alternating ${\text{Dy}}^{3+}$ and organic radicals. The magnetic molar susceptibility ${\ensuremath{\chi}}_{M}$ displays a strong angular variation for sample rotations around two directions perpendicular to the chain axis. A peculiar inversion between maxima and minima in the angular dependence of ${\ensuremath{\chi}}_{M}$ occurs on increasing temperature. Using information regarding the monomeric building block as well as an ab initio estimation of the magnetic anisotropy of the ${\text{Dy}}^{3+}$ ion, this ``anisotropy-inversion'' phenomenon can be assigned to weak one-dimensional ferromagnetism along the chain axis. This indicates that antiferromagnetic next-nearest-neighbor interactions between ${\text{Dy}}^{3+}$ ions dominate, despite the large Dy-Dy separation, over the nearest-neighbor interactions between the radicals and the ${\text{Dy}}^{3+}$ ions. Measurements of the field dependence of the magnetization, both along and perpendicularly to the chain, and of the angular dependence of ${\ensuremath{\chi}}_{M}$ in a strong magnetic field confirm such an interpretation. Transfer-matrix simulations of the experimental measurements are performed using a classical one-dimensional spin model with antiferromagnetic Heisenberg exchange interaction and noncollinear uniaxial single-ion anisotropies favoring a canted antiferromagnetic spin arrangement, with a net magnetic moment along the chain axis. The fine agreement obtained with experimental data provides estimates of the Hamiltonian parameters, essential for further study of the dynamics of rare-earth-based molecular chains.