Radio-frequency spectroscopy of the low-energy spectrum of the magnetic molecule Cr12Cu2

We present tunnel diode oscillator (TDO) measurements of dynamic magnetic susceptibility, inelastic neutron-scattering (INS) measurements, and theoretical predictions based on quantum Monte Carlo (QMC) calculations for a magnetic molecule system, Cr12Cu2. The TDO measurements show not only ground-state level crossings (as can also be observed in low-temperature dc magnetization measurements) but also clear evidence of crossings between certain excited energy levels. These TDO results are in excellent agreement with our theoretical predictions for a Heisenberg Hamiltonian and are further confirmed by our INS measurements. Our present findings demonstrate that the TDO technique is a valuable magnetic spectroscopic tool for studying magnetic molecules, and that the QMC method is a valuable tool for predicting properties of computationally demanding systems such as Cr12Cu2.