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The present work is aimed at the elaboration of the model of magnetic properties and magnetic relaxation in the mononuclear [Pc₂Tb]⁻TBA⁺ complex that displays single-molecule magnet properties. We calculate the Stark structure of the ground ⁷F₆ term of the Tb3+ ion in tHp pvrhangp rhargp model of the crystal field, taking account for covalence effects. The ground Stark level of die complex possesses the maximum value of the total angular momentum projection, while the energies of the excited Stark levels increase with decreasing │Mj│ values, thus giving rise to a barrier for the reversal of magnetization. The one-phonon transitions between the Stark levels of the Tb3+ ion induced by electron-vibrational interaction are shown to lead to magnetization relaxation in the [Pc₂Tb]⁻TBA⁺ complex. The rates of all possible transitions between the low-lying Stark levels are calculated in the temperature range 14 K

The low-temperature elementary spin excitations in the AFM molecular wheel Fe18 were studied experimentally by inelastic neutron scattering and theoretically by modern numerical methods, such as dynamical density matrix renormalization group or quantum Monte Carlo techniques, and analytical spin-wave theory calculations. Fe18 involves eighteen spin-5/2 FeIII ions with a Hubert space dimension of ˜1014, constituting a physical system that is situated in a region between microscopic and macroscopic. The combined experimental and theoretical approach allowed us to characterize and discuss the magnetic properties of Fe18 in great detail. It is demonstrated that physical concepts such as the rotational-band or L and E-band concepts developed for smaller rings are still applicable. In particular, the higher-lying low-temperature elementary spin excitations in Fe18 or AFM wheels, in general, are of discrete antiferromagnetic spin-wave character. [ABSTRACT FROM AUTHOR]