A Complete Ab Initio View of Orbach and Raman Spin–Lattice Relaxation in a Dysprosium Coordination Compound

Abstract

The unique electronic and magnetic properties of lanthanide molecular complexes place them at the forefront of the race toward high-temperature single-molecule magnets and magnetic quantum bits. The design of compounds of this class has so far being almost exclusively driven by static crystal field considerations, with an emphasis on increasing the magnetic anisotropy barrier. Now that this guideline has reached its maximum potential, a deeper understanding of spin-phonon relaxation mechanisms presents itself as key in order to drive synthetic chemistry beyond simple intuition. In this work, we compute relaxation times fully ab initio and unveil the nature of all spin-phonon relaxation mechanisms, namely Orbach and Raman pathways, in a prototypical Dy single-molecule magnet. Computational predictions are in agreement with the experimental determination of spin relaxation time and crystal field anisotropy, and show that Raman relaxation, dominating at low temperature, is triggered by low-energy phonons and little affected by further engineering of crystal field axiality. A comprehensive analysis of spin-phonon coupling mechanism reveals that molecular vibrations beyond the ion’s first coordination shell can also assume a prominent role in spin relaxation through an electrostatic polarization effect. Therefore, this work shows the way forward in the field by delivering a novel and complete set of chemically sound design rules tackling every aspect of spin relaxation at any temperature.

Understanding the magnetic anisotropy for linear sandwich [Er(COT)]+-based compounds: a theoretical investigation

“…The main thing to stress here is that both are approximate models which do not take into account the phonon density of states inside the crystal and the effective spin–phonon coupling of the spin-states with the molecular modes. Recently, Carretta and Sessoli et al 37,38 succeed in simulating both of Raman and Orbach relaxation processes of high performance Dy III -based SMMs. In this paper, the methods by Sessoli and Carretta are much more computational demanding, but the magnitude of the Orbach barrier has no relevance here.…”

Temperature Dependence of Spin–Phonon Coupling in [VO(acac)2]: A Computational and Spectroscopic Study

“…In a recent paper, some of us have shown for the [Dy(acac) 3 (H 2 O) 2 ] 58 complex that a large Sp-Ph coupling is found for those normal modes that can induce large polarization on the atoms of the first coordination sphere. Even in the case of [VO(acac) 2 ], such a statement is confirmed.…”

Terminal Ligand and Packing Effects on Slow Relaxation in an Isostructural Set of [Dy(H2dapp)X2]+ Single Molecule Magnets**

“…It was recently pointed out by Lunghi, Sessoli et al that low energy optical phonons are mostly responsible for the relaxation in lanthanide SMMs. [20] For (1) and ( 2) it could also be the result of opening optical phonon processes, as discussed by Gu and Wu, because of the peculiarity of the system with the π-stacking of the terminal nitrate ligands. [12a] In order to find a clear answer to this, further investigations such as theoretical calculations on the vibrational modes and Dy nuclear resonance vibrational spectroscopy (NRVS) are needed.…”