Nuclear-spin relaxation ofPb207in ferroelectric powders

Motivated by a recent proposal by Sushkov and co-workers [Phys. Rev. A 72, 034501 (2005); 73, 022107 (2006)] to search for a $P,T$-violating Schiff moment of the $^{207}\mathrm{Pb}$ nucleus in a ferroelectric solid, we have carried out a high-field nuclear magnetic resonance study of the longitudinal and transverse spin relaxation of the lead nuclei from room temperature down to $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for powder samples of lead titanate (PT), lead zirconium titanate, and a PT monocrystal. For all powder samples and independently of temperature, transverse relaxation times were found to be ${T}_{2}\ensuremath{\approx}1.5\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$, while the longitudinal relaxation times exhibited a temperature dependence, with ${T}_{1}$ of over an hour at the lowest temperatures, decreasing to ${T}_{1}\ensuremath{\approx}7\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ at room temperature. At high temperatures, the observed behavior is consistent with a two-phonon Raman process, while in the low-temperature limit, the relaxation appears to be dominated by a single-phonon (direct) process involving magnetic impurities. We discuss the implications of the results for the Schiff-moment search.