The low temperature spin dynamics of the single-molecule magnet [Mn 12 O 12 (CH 3 COOH) 16 (H 2 O) 4 ]⋅ 2CH 3 COOH·4H 2 O, hereafter Mn 12 Ac, were studied using High Frequency Electron Paramagnetic Resonance (HFEPR) in order to demonstrate magnetic quantum tunneling between resonant spin projection states. We prepare the spins such that they populate only one side of the axial potential energy barrier. Using a magnetic field we cause tunneling between resonant energy states. We then use HFEPR to monitor the populations on each side of the potential energy barrier. We can estimate the tunneling relaxation time between spin projection states by plotting the area of an EPR peak as a function of wait time at a resonance field. This technique provides an alternative method to magnetometry experiments for measuring spin relaxation dynamics.

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