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

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.

Pursuit of Record Breaking Energy Barriers: A Study of Magnetic Axiality in Diamide Ligated DyIII Single-Molecule Magnets

“…This phenomenon has been observed in other highly anisotropic lanthanide-based systems. 1,5,21,22 To complement this, the isotemperature magnetization curve at 1.9 K saturates at 5.28 μB mol -1 , further suggesting the well separated nature of the ground state ( Figure S3). Large separations between the ground state and excited states are highly sought after as it remains the origin for large spin reversal barriers, a necessary feature for the future incorporation of SMMs into technological devices.…”

“…The experimentally determined room temperature χT value is slightly smaller than the theoretical value, presumably due to the splitting of the 6 H15/2 ground state. 1 Upon cooling, the χT product remains relatively constant with only a slight decrease until 8 K, suggesting the presence of a well separated low-lying energy spectrum (vide infra). Below this temperature, the χT product rapidly drops, reaching a minimum value of 9.67 cm 3 Kmol -1 at 1.8 K. The abrupt decrease in the χT profile is indicative of magnetic blocking, where the system cannot reach an equilibrated population distribution due to the energy barrier to spin reversal.…”

“…Being able to design molecular species with defined magnetic axiality has allowed chemists to produce molecules possessing large energy barriers to spin reversal (Ueff) and, in some cases, magnetic blocking, reaching blocking temperatures (TB) as high as 20 K. 1 In that regard, those SMMs containing only a single metal center, single-ion magnets (SIMs), have recently garnered significant interest in the field of molecular magnetism, as the observed magnetic properties exist in the absence of magnetic exchange interactions, meaning that the experimentally determined performance of SIMs must arise from the combination of unquenched orbital angular momentum and crystal field contributions. This allows a tailored synthetic approach, which in recent years has evolved to include high symmetry crystal fields, [1][2][3] the introduction of main group ligands, 4 and the implementation of bulky ligands to obtain low coordination numbers. 5,6 However, the common theme among all of these systems is the devotion to harnessing the maximum magnetic anisotropy from the metal ion, especially if the metal is a lanthanide.…”

“…This finding is also in accordance with the ab initio determined energy of the first excited Kramers doublet which possess an energy of 414.6 cm -1 (vide infra); which is one of the largest separations observed between the ground state and excited states in any Dy III SMMs. 1,5,21,22 This large separation ensures that thermal relaxation will at least occur via this energy, yielding an impressive barrier to the slow relaxation of the magnetization.…”

Mononuclear Dysprosium(III) Complexes with Triphenylphosphine Oxide Ligands: Controlling the Coordination Environment and Magnetic Anisotropy

“…Since the ground KD are mostly ±15/2 state with small contributions from other states, these U calc values of 49.1 and 61.4 cm −1 for a and b, respectively, can be easily achieved upon application of a dc field. The absence of zero field SMM character can be directly attributed to the unfavorable ground state KD g zz alignment along the Dy-Cl bonds rather than the shorter Dy-O bonds of the TPPO ligands [12][13][14][15]. This is a consequence of the large number of Cl − ligands that would interact with the prolate Dy III electron density if g zz pointed along the desired Dy-O direction.…”