1 Introduction

This thesis presents recent muon spin rotation ($\mu {\cal SR}$)measurements of the low temperature electronic and magnetic properties of the known stoichiometric metallic alkali fullerides. The behaviour exhibited by these systems encompasses a wide variety of phenomena of contemporary interest in condensed matter physics. For example, the alkali fulleride superconductors are currently the highest temperature isotropic superconductors known. The only class of superconductor with higher critical temperatures (T_c) is the cuprates. Some alkali fulleride metals exhibit reversible solid-state polymerization. The polymeric phase may be effectively a 1 dimensional metal which in some cases undergoes a low temperature magnetic metal-insulator transition. The specific materials studied are the superconducting alkali fulleride salts of the form A₃C₆₀, with A = Rb, K and A₃ = Na₂Cs and the polymeric phases of the salts of the form A₁C₆₀, where A = K, Rb, Cs. The $\mu {\cal SR}$ technique, which is closely related to the widely known methods of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR or ESR), involves the use of the unstable positive muon as a sensitive local probe of magnetic and electronic structure.

Because of the great diversity of topics covered here, considerable reliance on major review articles is made, and a complete exposition of each topic has not been attempted.

Following introductions to the field of fullerenes and the specific topic of the metallic alkali fullerides, the technique is reviewed briefly in chapter 2, and some specific details of the experiments are given. In chapter 3, the theory of longitudinal field spin relaxation of muonium via the mechanism of spin-exchange with the conduction electrons is discussed, and the theory of the temperature dependence of this relaxation in superconductors is reviewed. Chapter 4 includes the results (and discussion thereof) of $\mu {\cal SR}$ experiments on the alkali fulleride superconductors. Chapter 5 is a brief summary of the theory of spin relaxation in zero applied field, an unfamiliar situation for most magnetic resonance techniques. Chapter 6 includes the results (and discussion thereof) of $\mu {\cal SR}$ experiments on the A₁C₆₀ alkali fullerides, and the conclusions are presented in chapter 7.