Nuclear Spin Relaxation in Dilute Magnetic Alloys: Kondo Systems and Spin Glasses.

Using Nozieres Fermi-liquid theory, a simple result, valid for temperatures T small compared to the Kondo temperature, is obtained which describes the effect of non-interacting (Kondo) magnetic impurities on the nuclear spin relaxation time T(,1) of a metal in the limit of small magnetic fields. Two generalization of this result to the case of finite magnetic fields are presented. In one case, we use a semi-phenomena -logical generalization of the ground state energy results of Ishii while in the other case, we employ the recent exact magnetization results of Andrei and Lowenstein, and Weigmann for a spin- 1/2 Kondo Hamiltonian. Both generalization show very reasonable agreement with the available experimental data. A number of experiments are suggested. In the second part of the thesis, we present two calculations for nuclear spin relaxation in spin glasses. In one of these calculations we use a time-dependent form of Edwards-Anderson mean field theory to get our nuclear magnetization recovery result in the spin glass phase. It is shown that most of the features of the available experimental data can be understood. Lastly, employing a Langevin equation approach, we derive a result, valid for temperatures T above the transition temperature T(,g), which shows that T(,1)('-1) diverges as (T - T(,g)).('-1) This appears to be in agreement with the very few data available.