Design of Single-Molecule Magnets: Insufficiency of the Anisotropy Barrier as the Sole Criterion.

摘要: Determination of the electronic energy spectrum a trigonalsymmetry mononuclear Yb3+ single-molecule magnet (SMM) by highresolution absorption and luminescence spectroscopies reveals that first excited doublet is placed nearly 500 cm−1 above ground one. Fitting paramagnetic relaxation times this SMM to thermally activated (Orbach) model {τ = τ0 × exp[ΔOrbach/(kBT)]} affords an activation barrier, ΔOrbach, only 38 cm−1. This result incompatible with spectroscopic observations. Thus, we unambiguously demonstrate, solely on the basis experimental data, Orbach cannot priori be considered as main mechanism determining spin dynamics SMMs. This study highlights fact general synthetic approach optimizing behavior maximization anisotropy barrier, intimately linked to the ligand field, sole parameter tuned, insufficient because complete neglect interaction magnetic moment molecule its environment. The expected dominant in cases which ligand field state below Debye temperature, typically low for molecular crystals and, thus, prevents use the anisotropy barrier design criterion realization high-temperature SMMs. Therefore, consideration additional design criteria address presence alternative processes beyond traditional double-well picture required.