Testing the radiation emanating from the molecular nanomagnet Fe8 during magnetization reversals

In the molecular nanomagnet Fe8 tunneling can occur from a metastable state to an excited state followed by a transition to the ground state. This transition is accompanied by an energy release with an equivalent frequency of 109.5 GHz. We constructed an experimental setup to measure whether this energy is released thermally or in the form of electromagnetic radiation. Contrary to a previous publication we find no evidence for release of electromagnetic radiation and place an upper limit of 5% on the total radiative energy released during the transition. The transitions between the first and second excited states to the ground state are consistent with a release of thermal energy alone. We also observe that the energy release extends for a longer time for the second excited state than for the first excited state.