A method to predict both the relaxation time of quantum tunneling of magnetization and the effective barrier of magnetic reversal for a Kramers single-ion magnet

In this work, a theoretical method for the prediction of both the relaxation time of quantum tunneling of magnetization (τQTM) and the effective barrier of magnetic reversal (Ueff) is proposed for single-ion magnet (SIM) systems of Kramers type. The reliability of theoretical τQTM is tested within a large series of 18 lanthanide SIMs. Compared to the experimental results, the deviations of theoretical τQTM are within one order of magnitude for 11 tested SIMs and the largest order-of-magnitude deviation is only 1.86. In the aspect of Ueff, for 5 typical high-performance Dy-SIMs of the local coordination mode of a pentagonal bipyramid, the relative deviations of theoretical values lie within the range of 1.4-7.2%. Thus this method possesses good reliability, at least in the aspect of the order of magnitude. Besides an empirical estimate of the local magnetic field experienced by the central ion, for a given SIM, one ab initio calculation, providing accurate g-factors of both ground and excited Kramers doublets (KDs), is the only computational cost. Therefore this method has a high degree of both reliability and efficiency. Based on the temperature dependence of theoretically predicted Ueff and its contributions from various KDs, some mechanistic information on the magnetic relaxation could be given by this method too. Therefore it is reasonable to expect the bright prospect of this method in the aspects of both the interpretation of the existing experimental results and rational design of future high-performance SIMs.