Zero-and low-field spin relaxation studied by positive muons

Zero- and low-field spin-relaxation functions have been studied for the first time by using positive muons, and results are compared with the stochastic theory of low-field relaxation formulated by Kubo and Toyabe. The dipolar broadening of the zero-field relaxation has been studied in detail. In Zr${\mathrm{H}}_{2}$, the zero-field relaxation function of ${\ensuremath{\mu}}^{+}$ has been found to decay ${(5)}^{\mathrm{\textonehalf{}}}$ times faster than the high-field relaxation function, which is explained in terms of the contribution of the nonsecular part of the dipolar interaction. Advantages of the zero-field method over the conventional muon-spin rotation method in practical applications, especially for studies of the ${\ensuremath{\mu}}^{+}$ diffusion/trapping, are discussed.