Fine-tuning the local symmetry to attain record blocking temperature and magnetic remanence in a single-ion magnet

Abstract

Remanence and coercivity are the basic characteristics of permanent magnets. They are also tightly correlated with the existence of long relaxation times of magnetization in a number of molecular complexes, called accordingly single-molecule magnets (SMMs). Up to now, hysteresis loops with large coercive fields have only been observed in polynuclear metal complexes and metal-radical SMMs. On the contrary, mononuclear complexes, called single-ion magnets (SIM), have shown hysteresis loops of butterfly/phonon bottleneck type, with negligible coercivity, and therefore with much shorter relaxation times of magnetization. A mononuclear ErIII complex is presented with hysteresis loops having large coercive fields, achieving 7000?Oe at T=1.8?K and field variation as slow as 1?h for the entire cycle. The coercivity persists up to about 5?K, while the hysteresis loops persist to 12?K. Our finding shows that SIMs can be as efficient as polynuclear SMMs, thus opening new perspectives for their applications. A record blocking capability of a single-ion magnet has been predicted and obtained. Ab?initio calculations on the Er and the isostructural Dy analogue allowed deeper insight into the reasons for the strong magnetic blocking, explaining the striking differences between magnetic behaviors of these two compounds. Dashed line: Calculated orientation of the main magnetic axis in the ground and first excited Kramers doublet. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.