Lineshape of magnetodipole transitions and magnetization relaxation in Mn12Ac

The lineshapes of the crystal-field vertical bar ±10>→ vertical bar ±9> transitions in Mn12Ac are found to be symmetric Gaussians for the non-magnetized state and asymmetric for the magnetized state, even in zero magnetic field. This is explained by inhomogeneous broadening combined with a contribution of off-diagonal components of the magnetic susceptibility to the effective permeability (Voigt geometry). Relaxation of the vertical bar ±10> state populations and quantum tunnelling of the magnetization were observed in frequency-swept magnetic resonance spectra at fixed fields