Symmetry-Supported Magnetic Blocking at 20 K in Pentagonal Bipyramidal Dy(III) Single-Ion Magnets

TLDR

Single‑molecule magnets that can be trapped in one of two bistable magnetic states separated by an energy barrier are promising for high‑density storage, quantum processing, and spintronics, yet fast quantum tunnelling of magnetization limits their relaxation times. The study aims to suppress quantum tunnelling of magnetization by exploiting pentagonal bipyramidal symmetry in Dy(III) single‑ion magnets. We synthesized Dy(Cy3PO)2(H2O)5X3·(Cy3PO)·H2O·EtOH (X = Cl, Br) and characterized their magnetic behavior. The compounds exhibit large energy barriers of 472 K (1) and 543 K (2) and a record magnetic hysteresis temperature of 20 K for 2, confirming that symmetry can dramatically enhance single‑ion magnet performance.

Abstract

Single-molecule magnets (SMMs) that can be trapped in one of the bistable magnetic states separated by an energy barrier are among the most promising candidates for high-density information storage, quantum processing, and spintronics. To date, a considerable series of achievements have been made. However, the presence of fast quantum tunnelling of magnetization (QTM) in most SMMs, especially in single-ion magnets (SIMs), provides a rapid relaxation route and often sets up a limit for the relaxation time. Here, we pursue the pentagonal bipyramidal symmetry to suppress the QTM and present pentagonal bipyramidal Dy(III) SIMs [Dy(Cy3PO)2(H2O)5]Cl3·(Cy3PO)·H2O·EtOH (1) and [Dy(Cy3PO)2(H2O)5]Br3·2(Cy3PO)·2H2O·2EtOH (2), (Cy3PO = tricyclohexyl phosphine oxide). Magnetic characterizations reveal their fascinating SMM properties with high energy barriers as 472(7) K for 1 and 543(2) K for 2, along with a record magnetic hysteresis temperature up to 20 K for 2. These results, combined with the ab initio calculations, offer an illuminating insight into the vast possibility and potential of what the symmetry rules can achieve in molecular magnetism.