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Second-order nuclear magnetic relaxation associated with electric quadrupole interaction between paramagnetic centers and two-level systems is studied. First- and second-order relaxation times are compared. It is shown that second-order relaxation prevails in relatively low magnetic fields.

The problem of obtaining the nuclear spin interaction Hamilton operator via magnon field in ferromagnets is discussed by consecutive canonic transformation method. Using this method the one magnon nuclear spin interaction in any order of perturbation theory is taken into account. The indirect spin interact,ion Hamilton operator constant obtained is compared with the well known Suhl-Nakamura interaction constant. It is shown, that in the second order of perturbation theory these results coincide. MeTOnOM nOCJlenOBaTeJIbHblX IntroduetionThe consecutive canonic transformation method has been suggested in [l to 31 in order t o obtain the indirect spin interaction via the phonon field.The spin system Hamiltonian interacting with the phonon field has the form(1)where Hal, Ho, are the Haniiltonians of the spin and phonon subsystems, respectively, V is their interaction operator. The traditional method of obtaining the indirect spin interaction operator consists of two stages : I n the first stage, the canonic transformation

The low temperature properties of amorphous solids and some other disordered systems have been described within the model of special-type structural excitations called two-level systems (TLS). According to the model, some atoms (or a group of atoms), occupying one of two adjacent minima separated with a barrier, are assumed to tunnel quantum-mechanically to the other minimum I l l .The influence of TLS on the magnetic properties of amorphous solids and other disordered materials has been investigated in 12 to 71. For instance the influence of TLS of nuclear and electron spin-lattice relaxation processes has been considered in I 4 to 71.In the present note we propose the possibility of indirect saturation of nuclear sublevels under the influence of ultrasound in disordered materials containing paramagnetic impurities. The saturation occurs because of the coupling between the nuclear spins and pseudospins of TLS .It is feasible to determine the structure of the TLS surrounding the paramagnetic impurity by this method.