Single-Molecule Toroic Design through Magnetic Exchange Coupling

• Published in: Matter Vol. 2; no. 6; pp. 1481 - 1493
• Main Authors: Zhang, Hao-Lan, Zhai, Yuan-Qi, Qin, Lei, Ungur, Liviu, Nojiri, Hiroyuki, Zheng, Yan-Zhen
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 03.06.2020
• Subjects: ab initio calculation; EPR spectroscopy; macrocycle; MAP1: Discovery; single-molecule toroic; toroidal magnetic moment; ab initio calculation; macrocycle; toroidal magnetic moment; MAP1: Discovery; single-molecule toroic; EPR spectroscopy
• ISSN: 2590-2385; 2590-2385
• DOI: 10.1016/j.matt.2020.02.021

Toroidal molecular magnets represent promising candidates for next-generation ultra-dense information storage. These wheel-like molecules are able to store one bit per molecule because of their insensitivity to homogeneous magnetic fields—one of the main sources of magnetic perturbations. However, synthesis of molecules possessing a well-defined and stable vortex arrangement of the on-site magnetic moments in the ground state represents a challenge. Here, we show that 16 magnetic metal ions can be alternately arranged into a macrocycle named {Fe8Dy8}. The net toroidal moment can be experimentally determined at 0.23 Tesla. Moreover, ab initio calculations were performed to reveal that ferromagnetic exchange interactions between the FeIII and DyIII metal centers are the key to generate this toroidal moment. This feature is significantly distinguished from the previously described dipole-dipole interaction-based single-molecule toroics (SMTs), showing the importance of exchange-coupling interactions in the design of next-generation SMTs. [Display omitted] •An exchange interaction-based single-molecule toroic named {Fe8Dy8} is synthesized•The magnitude of exchange coupling for generating the toroidal moment is determined•The toroidal ground state is 4-fold degenerated, which is unprecedented in SMTs•The energy gap between the ground and the first excited states is determined by EPR The big data era calls for larger capacity of our hard drive, which in turn depends on the number of magnetic units that store bits of 1 or 0. However, as the density of these units increases, flipping one unit without affecting another becomes more difficult because of undesired magnetic perturbations from the reading/writing heads. Single-molecule toroics (SMTs) that exploit vortex-like magnetic structures are insensitive to homogeneous magnetic fields and hence are promising for next-generation ultra-dense information storage. However, the synthesis of such molecular materials is challenging. Here, we show by using ferromagnetic interactions that this target can be realized in a 16-membered heterometallic cluster {Fe8Dy8}, which shows a stable 4-fold degenerated magnetic toroidal ground state at low temperatures. This is significantly distinguished from the most studied dipole-dipole interaction-based SMTs and demonstrates a promising strategy for the next generation of SMT design. A circular molecule named {Fe8Dy8} with fixed toroidal magnetic moment below a certain temperature can be used for high-density information storage. The energy gap between this toroidal ground state (blue molecule) and the first excited state (reddish molecule) causes the S-shaped magnetization plot at low field, while such a toroidal moment is caused by the ferromagnetic exchange interaction between the metal centers. The strong magnetic anisotropy of the dysprosium(III) ions determines the toroidal directions (arrows in the molecular wheel).