The coexistence of long τQTM and high Ueff as a concise criterion for a good single-molecule magnet: a theoretical case study of square antiprism dysprosium single-ion magnets

A systematic theoretical study is performed on a group of 16 square antiprism dysprosium single-ion magnets. Based on ab initio calculations, the quantum tunneling of magnetization (QTM) time, i.e., tau(QTM), and effective barrier of magnetic reversal, U-eff, are theoretically predicted. The theoretical tau(QTM) is able to identify the ones with the longest QTM time with small numerical deviations. Similar results occur with respect to U-eff too. The systems possessing the best single-molecule magnet (SMM) properties here are just the ones having both the longest tau(QTM) and the highest U-eff, from either experiment or theory. Thus, our results suggest the coexistence of long tau(QTM) and high U-eff to be a criterion for high-performance SMMs. Although having its own limits, this criterion is easy to be applied in a large number of systems since both tau(QTM) and U-eff could be predicted by theory with satisfactory efficiency and reliability. Therefore, this concise criterion could provide screened candidates for high-performance SMMs quickly and, hence, ease the burden of further exploration aiming for a higher degree of precision. This screening is important since the further exploration could easily demand tens or even hundreds of ab initio calculations for a single SMM. A semi-quantitative crystal field (CF) analysis is performed and shown here to be capable of indicating the general trends in a more chemically intuitive way. This analysis could help to identify the most important coordinating atoms for both diagonal and non-diagonal CF components. Thus, it could give some direct clues for improving the SMM properties: reducing the distance of the axial atom to the central ion, rotating the axial atom closer to the easy axis or increasing the amount of its negative charge. Correspondingly, opposite operations on the equatorial atom could give the same result.

Automated summary

A systematic theoretical study was conducted on a group of 16 square antiprism dysprosium single-ion magnets. The study predicted the quantum tunneling of magnetization (QTM) time and effective barrier of magnetic reversal (U-eff) based on ab initio calculations. The results suggest that the coexistence of long QTM time and high U-eff is a criterion for high-performance single-molecule magnets (SMMs), and a semi-quantitative crystal field analysis can provide guidance for improving SMM properties.