Probing Magnetic Excitations in CoII Single‐Molecule Magnets by Inelastic Neutron Scattering

Abstract

Co(acac)2(H2O)2 (1, acac = acetylacetonate), a transition metal complex (S = 3/2), displays field‐induced slow magnetic relaxation as a single‐molecule magnet. For 1 and its isotopologues Co(acac)2(D2O)2 (1‐d4) and Co(acac‐d7)2(D2O)2 (1‐d18) in approximately D4h symmetry, zero‐field splitting of the ground electronic state leads to two Kramers doublets (KDs): lower energy MS = ±1/2 (ϕ1,2) and higher energy MS = ±3/2 (ϕ3,4) states. This work employs inelastic neutron scattering (INS), a unique method to probe magnetic transitions, to probe different magnetic excitations in 1‐d4 and 1‐d18. Direct‐geometry, time‐of‐flight Disk‐Chopper Spectrometer (DCS), with applied magnetic fields up to 10 T, has been used to study the intra‐KD transition as a result of Zeeman splitting, MS = –1/2 (ϕ1) → MS = +1/2 (ϕ2), in 1‐d18. This is a rare study of the MS = –1/2 → MS = +1/2 excitation in transition metal complexes by INS. Indirect‐geometry INS spectrometer VISION has been used to probe the inter‐KD, ZFS transition, MS = ±1/2 (ϕ1,2) → MS = ±3/2 (ϕ3,4) in both 1‐d4 and 1‐d18, by variable‐temperature (VT) properties of this excitation. The INS spectra measured on VISION also give phonon features of the complexes that are well described by periodic DFT phonon calculations.