Nuclear relaxation induced by a paramagnetic impurity

The paper deals with investigation of nuclear spin-lattice relaxation, caused by a paramagnetic impurity with a singlet ground state. The results show that contributions of two-step resonance processes are not taken into account in the formulas for the rate of nuclear relaxation due to paramagnetic impurity. Inparticular, there are two-step resonance transitions which produce a supplementary contribution to the relaxation rate exactly equal to that of direct processes. In hamiltonian of electron-nuclear interaction the author restricts himself with operators describing the nuclear spin flip which is hot accompanied with the electron spin flip. It is noted that the direct two-step resonance processes of the Orbakh-Aminov type at which the finite state of an electron coincides with the initial one are particularly important in relaxation of a nucleus by a magnetic ion with a singlet ground state