Giant spin-phonon bottleneck effects in evaporable vanadyl-based molecules with long spin coherence

Article abstract of DOI:10.1039/c6dt02559e

Vanadium(iv) complexes have recently shown record quantum spin coherence times that in several circumstances are limited by spin-lattice relaxation. The role of the environment and vibronic properties in the low temperature dynamics is here investigated by a comparative study of the magnetization dynamics as a function of crystallite size and the steric hindrance of the β-diketonate ligands in VO(acac)₂ (1), VO(dpm)₂ (2) and VO(dbm)₂ (3) evaporable complexes (acac^- = acetylacetonate, dpm^- = dipivaloylmethanate, and dbm^- = dibenzoylmethanate). A pronounced crystallite size dependence of the relaxation time is observed at unusually high temperatures (up to 40 K), which is associated with a giant spin-phonon bottleneck effect. We model this behaviour by an ad hoc force field approach derived from density functional theory calculations, which evidences a correlation of the intensity of the phenomenon with ligand dimensions and the unit cell size.