A Stable Pentagonal Bipyramidal Dy(III) Single-Ion Magnet with a Record Magnetization Reversal Barrier over 1000 K

TLDR

Single‑molecule magnets with large spin‑reversal barriers exhibit slow magnetic relaxation and hysteresis, yet synthesizing highly stable SMMs with both large barriers and long relaxation times remains challenging. Micro‑SQUID measurements of undiluted single crystals revealed weak intermolecular interactions, and magnetic‑relaxation studies showed thermally activated quantum tunneling through the third excited Kramers doublet driven by enhanced axial and reduced transverse anisotropy. The two neutral Dy(III) pentagonal bipyramidal complexes display SMM behavior with pronounced hysteresis up to 14 K and an unprecedented effective barrier of 1025 K.

Abstract

Single-molecule magnets (SMMs) with a large spin reversal barrier have been recognized to exhibit slow magnetic relaxation that can lead to a magnetic hysteresis loop. Synthesis of highly stable SMMs with both large energy barriers and significantly slow relaxation times is challenging. Here, we report two highly stable and neutral Dy(III) classical coordination compounds with pentagonal bipyramidal local geometry that exhibit SMM behavior. Weak intermolecular interactions in the undiluted single crystals are first observed for mononuclear lanthanide SMMs by micro-SQUID measurements. The investigation of magnetic relaxation reveals the thermally activated quantum tunneling of magnetization through the third excited Kramers doublet, owing to the increased axial magnetic anisotropy and weaker transverse magnetic anisotropy. As a result, pronounced magnetic hysteresis loops up to 14 K are observed, and the effective energy barrier (Ueff = 1025 K) for relaxation of magnetization reached a breakthrough among the SMMs.