Does macroscopic quantum coherence occur in ferritin?

S. Gider et al. (1) studied classical and quantum magnetic phenomena in natural and artificial ferritin proteins. If the magnetic moment of the ferritin molecules is blocked below 5 K, as Gider et al. show in figures 1 and 2 of their report (1), then the observed resonance at 24.3 mK, shown in figure 3 of their report, cannot be attributed to quantum oscillations of the magnetic moment between two equilibrium orientations, as stated by Gider et al. To clarify this point one should consider the time-dependent magnetism of a single domain particle. In the absence of a magnetic field, the energy of a single domain particle is minimized when its magnetic moment aligns with the anisotropy axis of the particle with the two opposite orientations being equivalent. These two orientations are separated by an energy barrier, U, where U = KV, where V is the volume of the particle and K the magnetic anisotropy constant characteristic of the material. The overbarrier transition at temperature T is