ABSTRACT
This chapter presents a very crude description of the basic nuclear magnetic resonance (NMR) experiments, compared to their muon equivalent. It leads onto a re-discussion of a few fundamental concepts, like longitudinal and transverse relaxation, in a language slightly different from that most familiar to the muon community. The chapter considers critical fluctuations in simple antiferromagnets, the classic example where NMR first proved its merits when opening up the field and muon spin research (μSR) later added renewed insight. The chapter also considers the effect of the spin interaction with electrons in simple metals, treated as a free electron gas. The derivation of the Knight shift and of Korringa relaxation may be extended from the Fermi gas to the Fermi liquid case, with essentially the same results. The peculiar aspects of nuclear relaxation in the superconducting state were considered one of the first direct experimental evidences of the validity of the BCS theory.
