Introduction

In chapter 1 we introduced the s-d and the Anderson models as the basic models for magnetic impurities in simple metallic hosts. In the succeeding chapters we have outlined techniques for predicting the static and dynamic behaviour of these models over most of the possible parameter regimes. These techniques give results which are either exact or which are within well controlled approximations (for a detailed summary of these results see appendix K). We know from the comparisons between theory and experiment which we have made so far, that the physical picture which emerges is in broad agreement with the experimental observations. The parameter regime of primary interest is the Kondo regime where there is local moment behaviour at high temperatures or high magnetic fields with a Curie law susceptibility. This undergoes a broad transition or crossover at temperatures of the order TK (in weak or zero fields) to Fermi liquid behaviour and a Pauli susceptibility at low temperatures. The lnT contributions calculated by Kondo explain the resistance minimum, and the Fermi liquid theory gives the power law behaviour of the resistance at very low temperatures. The narrow peak in the one electron density of states, the Kondo resonance, qualitatively explains the basic trends in the change in thermodynamic behaviour with temperature, such as the peak in the specific heat.