The impact of spin-vibrational coupling on magnetic relaxation of a Co() single-molecule magnet

Single-molecule magnets (SMMs) based on transition metals have appeared as enticing targets exploiting magnetic anisotropy in 3d elements. Among transition metals, Co based SMMs are very prominent as they often exhibit a high spin-reversal barrier ( U eff ), owing to their large unquenched orbital a...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2023-05, Vol.25 (21), p.14848-14861
Main Authors: Nain, Sakshi, Kumar, Manish, Ali, Md. Ehesan
Format: Article
Language:English
Subjects:
Angular momentum
Coupling (molecular)
Magnetic anisotropy
Magnetic induction
Magnetic relaxation
Magnetization
Magnets
Quantum tunnelling
Transition metals
Vibration mode
Wave functions
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Summary:Single-molecule magnets (SMMs) based on transition metals have appeared as enticing targets exploiting magnetic anisotropy in 3d elements. Among transition metals, Co based SMMs are very prominent as they often exhibit a high spin-reversal barrier ( U eff ), owing to their large unquenched orbital angular momentum. Employing the wave function-based multireference CASSCF/NEVPT2 calculations, herein we substantiate the zero-field splitting parameters of four mononuclear Co complexes and one of them has shown potential as an SMM. The mechanism of magnetic relaxation has been studied to understand the molecular origin of the slow relaxation of magnetization. The combination of suppressed quantum tunneling of magnetization (QTM) at the ground state and the high negative D value usually manifests SMM behavior in a zero-applied magnetic field. However, mere fulfillment of these conditions ensures little about their SMM behavior, as spin-vibrational coupling often plays spoilsport by lowering the spin relaxation channels. A detailed study accounting for all the 46 vibrational modes below the first-excited state for the prospective Co( ii ) complex, reveals one of the vibrational modes providing a lower spin relaxation pathway. This results in the development of an SMM with a U eff value of 239.30 cm −1 , decreased by ∼81 cm −1 from the value without spin-vibrational coupling. The spin-vibrational coupling affects the magnetization reversal barrier height of SMMs. This has been observed and quantified in a Co( ii ) Kramer's system with non-Aufbau ground state occupation.
ISSN:1463-9076
1463-9084
DOI:10.1039/d3cp01243c