Acoustic nuclear resonance in LiF impure crystals

In order to elucidate the 'defect' mechanism of the nuclear quadrupole spin-phonon coupling, investigations have been made of the acoustic saturation of the quadrupole transitions of the Li7 nuclei in LiF crystals doped with cobalt and magnesium to weight concentrations of about 0.1%, with a concurrent measurement of the spin-lattice relaxation time T1. In crystals containing the nonparamagnetic ions Mg2+, the relaxation time Tsub(i) has been found to increase with the increasing impurity concentration, the effect of the acoustic nuclear resonance remaining, however, practically unchanged. At the same time, in crystals doped with cobalt the effective probability of ultrasonic transitions has been observed to increase to a value about 20 times as high as that for a pure crystal. This is regarded as a direct manifestation of the 'defect' mechanism, in which the paramagnetic ions Co2+ play the part of sources of strengthened dynamical gradients of the electric field induced in a sound wave on the neares Li7 nuclei. The paper discusses a possible mechanism of formation of these gradients in the neighbourhood of a paramagnetic impurity and the influence of its paramagnetism upon the diffusion barrier, which determines the effectiveness of propagation of a local disturbance through the crystal as a spin diffusion, and upon the acoustic solid-effect