Role of the transition state in muon implantation

Abstract

In muon-spin-rotation experiments, positive muons are implanted in the material and come to rest in the unrelaxed host lattice. The formation of the final configuration requires a lattice relaxation which does not occur instantly. The present paper is concerned with the transition from the initial stopping state to the final muon configuration. We identify the often observed fast relaxing signal in muon experiments (e.g., in several oxides studied recently) with the transition state in this conversion process. This state is paramagnetic with a small hyperfine interaction (in the order of MHz) which fluctuates and averages to almost zero. Because of its apparent diamagnetic frequency behavior, the fast signal was in the past assigned to ${\mathrm{Mu}}^{+}$ or ${\mathrm{Mu}}^{\ensuremath{-}}$. We present evidence that this state is actually paramagnetic. The model presented in this paper is of importance for the interpretation of past and future $\ensuremath{\mu}\mathrm{SR}$ measurements.