Chapter 9 Diffusion and Relaxation of Nuclear Spins in Crystals Containing Paramagnetic Impurities

Abstract

Publisher Summary This chapter focuses on the results of the nuclear relaxation theory in a nonmetallic diamagnetic crystal containing a magnetic impurity and of a comparison of the results of the theory with the latest experimental data. In this chapter the nuclear magnetic relaxation will be considered in a nonmetallic diamagnetic crystal with a small concentration of paramagnetic atoms. Some of such samples are: 1) a diluted paramagnetic salt (for example, lanthanum magnesium nitrate, in which a small fraction of the La atoms has been replaced by atoms of Nd or Ce), 2) an oxide or a halide of a nontransition metal with a transition metal impurity (for example, ruby,that is A1 2 ,0 3 with an admixture of Cr 2 O 3 ), 3) an alkali halide crystal with F-centres, and 4) a crystal containing free radicals. The concept of nuclear spin diffusion has been also introduced in this chapter. They have shown that spin diffusion is important in the nuclear relaxation in a diamagnetic crystal containing a small concentration of magnetic impurity. Later it has been shown that spin diffusion is also essential for dynamic polarization of nuclei (the so-called solid effect) in such a crystal. Because of the fact that the method of dynamic polarization is the most powerful method for polarization of light nuclei, the study of the nuclear spin diffusion and relaxation has become of considerable interest.