The Influence of Electron-Withdrawing Groups on the Relaxation Time of Field-Induced Er(III) Single Molecule Magnets.

Abstract

Single molecule magnetism (SMM) presents a novel avenue for the pursuit of a bottom up approach to the design of next generation magnets, their molecular origin of magnetism and sensitivity to their chemical environment allows SMMs to be designed and exploited at the molecular level1. Applications include proposals for SMMs to be used as qubits and components in spintronic devices2,3. Here we present the synthesis and magnetic properties of mononuclear Ln(III) complexes, where two Er(III) complexes exhibit SMM behavior and blocking temperatures of around 40K.4 We used a synthetic approach and ligand fine-tuning where the ligand field is favorable for the Er(III) compounds to exhibit SMM properties.Single crystal structure analysis was carried out to obtain structural information on all the presented complexes. The field dependence of the magnetization for both Er(III) compounds were measured at 2, 3 and 5 K; the magnetization curves did not saturate at high fields indicating the presence of significant magnetic anisotropy and/or low-lying excited states. In order to investigate the potential presence of slow relaxation of the magnetization caused by SMM behavior, ac magnetic susceptibility measurements were performed, in applied dc-fields from 0 to 3000 Oe, in attempts to suppress any quantum tunneling of the magnetization (QTM). For both compounds the in-phase and out-of-phase ac susceptibility show field-dependent signals; the optimum field was found to be 500 Oe and this was used for further ac measurements. In both cases, the ac measurements reveal temperature dependent in- and out-of-phase signals with clear maxima up to 3.5 K. The maxima of the frequency dependent out-of-phase susceptibility curves were used extract the relaxation time as a function of temperature. **