Dipolar Coupling as a Mechanism for Fine Control of Magnetic States in ErCOT-Alkyl Molecular Magnets

Abstract

The design of molecular magnets has progressed greatly by taking advantage of the ability to impart successive perturbations and control vibronic transitions in 4f n systems through the careful manipulation of the crystal field. Herein, we control the orientation and rigidity of two dinuclear ErCOT-based molecular magnets: the inversion-symmetric bridged [ErCOT(μ-Me)(THF)] 2 (2) and the nearly linear Li[(ErCOT) 2 (μ-Me) 3 ] (3). The conserved anisotropy of the ErCOT synthetic unit facilitates the direction of the arrangement of its magnetic anisotropy for the purposes of generating controlled internal magnetic fields, improving control of the energetics and transition probabilities of the electronic angular momentum states with exchange biasing via dipolar coupling. This control is evidenced through the introduction of a second thermal barrier to relaxation operant at low temperatures that is twice as large in 3 as in 2. This barrier acts to suppress through-barrier relaxation by protecting the ground state from interacting with stray local fields while operating at an energy scale an order of magnitude smaller than the crystal field term. These properties are highlighted when contrasted against the mononuclear structure ErCOT(Bn)(THF) 2 (1), in which quantum tunneling of the magnetization processes dominate, as demonstrated by magnetometry and ab initio computational methods. Furthermore, far-infrared magnetospectroscopy measurements reveal that the increased rigidity imparted by successive removal of solvent ligands when adding bridging methyl groups, along with the increased excited state purity, severely limits local spin− vibrational interactions that facilitate magnetic relaxation, manifesting as longer relaxation times in 3 relative to those in 2 as temperature is increased.

Cycloheptatrienyl-Bridged Triple-Decker Complexes

“…The nearly parallel alignment of the anisotropy axes of the ground doublets in 2-Er suggests the presence of ferromagnetic dipolar coupling between the ions, which is typically observed for two colinear axes that are also parallel to the interconnecting vector . However, ferromagnetic coupling is in stark contrast to the experimental χ M T ( T ) and M ( H ) data, clearly indicating antiferromagnetic interactions.…”

Magnetic behaviour of a spin-canted asymmetric lanthanide quinolate trimer

“…, barriers, relaxation, QTM, differ from their single ion characteristics drastically. Often, for polynuclear complexes their electronic properties can be enhanced when all metallic ions are anisotropic with parallel or nearly parallel arrangements of spins, 36,80–82 while for non-colinear arrangements it has been usually observed that the properties are diminished. 38,58,83 In contrast, the interaction of the three Dy( iii ) ions in [Dy 3 (hq) 7 (NO 3 ) 2 (H 2 O)] along with the canted spin arrangements, leads to a spin ground state with anisotropic characteristics and open loops and slow relaxation at zero field.…”

“…To further the development of favourable SMM properties and finally implement lanthanide-based molecules in devices, a detailed understanding of their magnetic properties continues to be a critical step. 28–31 A great deal of work has shed some light on the understanding of the magnetic behaviour of single lanthanide ion molecules, 32–38 denoting the importance of the role of magnetic interaction in SMMs. This understanding is required since polymetallic lanthanide clusters can show some unusual physical properties such as the observation of a toroidal magnetic 39–41 and strong magnetic exchange, causing an increment of the blocking temperatures.…”

Record Quantum Tunneling Time in an Air-Stable Exchange-Bias Dysprosium Macrocycle

“…As such, the parameter of total magnetic interaction, −2.45 cm –1 , is very close to that determined by μ-SQUID, suggesting that a dominant dipolar coupling induces exchange biasing. From the spectrum of the low-lying exchange multiplets (Table S17), the energy gap between the lowest two exchanged KDs was determined to be 1.225 cm –1 , which is sufficient to suppress the QTM process …”