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

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.

具备大自旋反转势垒的单分子磁体（Single-molecule magnets, SMMs）已被证实可表现出缓慢的磁弛豫行为，进而产生磁滞回线。同时兼具大自旋反转势垒与极长弛豫时间的高稳定性单分子磁体的合成极具挑战性。本工作报道了两种具备五角双锥局域几何构型的高稳定性中性镝(III)经典配位化合物，二者均表现出单分子磁体行为。通过微超导量子干涉装置（micro-SQUID）测量，我们首次在单核镧系单分子磁体的未稀释单晶中观测到弱分子间相互作用。磁弛豫研究表明，由于轴向磁各向异性增强且横向磁各向异性减弱，磁化过程通过第三激发态Kramers二重态（Kramers doublet）发生热激活的磁化量子隧穿。最终，我们观测到最高可达14 K的显著磁滞回线，其磁化弛豫有效能垒（Ueff = 1025 K）在单分子磁体领域实现了突破性进展。