Tailoring single-ion magnet properties of coordination polymer C11H18DyN3O9 (Dy-CP) using Radial Effective Charge model (RECM) and Superposition model (SPM)

Abstract

We investigate Dy-based coordination polymer C11H18DyN3O9 (Dy-CP) exhibiting single-ion magnet (SIM) properties, e.g., quantum tunnelling of magnetization (QTM), magnetic anisotropy, magnetic relaxation, and effective energy barrier (Ueff). To elucidate the underlying mechanisms, crystal field parameters (CFPs) for Dy3+ ions were modelled using radial effective charge model (RECM) and superposition model (SPM), and computational packages SIMPRE and SPECTRE. The modelled CFPs enable predicting energy levels and associated wave functions, which successfully explain the field-induced Dy-CP SIM properties. So calculated magnetic susceptibility and isothermal magnetization match experimental data reasonably well. The smaller energy separations of the first (Δ0-1 ~31 cm-1) and the second (Δ0-2 = 74 cm-1) excited Kramers doublets suggest small Ueff = 65 cm-1 for Dy-CP. The magnetic moments of Dy3+ ions exhibit an easy-axis type magnetic anisotropy in the ground state, but change orientation in the excited states due to mixing of states from different Kramers doublet. Low-symmetry CF components play crucial role in connecting different |±MJ> states within the ground multiplet, resulting in QTM and magnetic relaxation to the ground state occurring via the excited states. The RECM and SPM calculated CFP sets are standardized employing the 3DD package to enable meaningful comparison and assessing their mutual equivalence. The results demonstrate the correlation between structural and electronic features of the molecule and site symmetry and distortion of the local coordination polyhedra with SIM properties, offering insights for rational design of new SIMs. The importance of considering low-symmetry aspects in CFP modelling for accurate predictions of magnetic properties is highlighted. This study provides deeper understanding of field-induced behavior in rare-earth-based SIMs and approaches for rationalization of experimentally measured SIMs’ properties.