Temperature-Independent Spin-Lattice Relaxation Time in Metals at Very Low Temperatures

The formalism of nuclear spin-lattice relaxation at low temperatures is developed, leading to a new relaxation time $T_{\mu }$ and a straightforward method of interpreting very-low-temperature relaxation data. Data for ${}_{}{}^{60}{}_{}{}^{}\mathrm{Co}$ in Fe, Ni, and Co hosts and for ${}_{}{}^{56}{}_{}{}^{}\mathrm{Co}$ in Fe are summarized. The use of NMR in oriented nuclei for determining relaxation times is discussed, and some comments are made on the role of frequency modulation in NMR experiments with oriented nuclei.