High-Sensitivity Electron Paramagnetic Resonance ofMn12-Acetate

The energy diagram of ${\mathrm{Mn}}_{12}$-acetate is probed close to the top of the anisotropy barrier using a novel, high-sensitivity, electron paramagnetic resonance technique. Multiple resonances, and their temperature dependence, are observed from 35 to 115 GHz, for a single high-quality crystal. The data are sufficiently detailed to make extremely accurate comparisons with predictions based on a spin $S=10\mathrm{}$ Hamiltonian. Although overall agreement is good, we find evidence for possible inadequacies of this model.