Nuclear Magnetic Relaxation of Domain-Wall Nuclear Spins via Magnon Interactions in Fe

Measurements of the longitudinal and transverse relaxation rates of ${\mathrm{Fe}}^{57}$ nuclei in the domain walls of natural and enriched Fe have been made over the temperature range 1.2-295°K by use of spin-echo techniques. The relaxation times are found to vary with position in the wall as $\frac{T_0}{{sech}^{2}x}$, where $x$ is the distance from the center of the wall (measured in wall-width units) and $T_0$ is the shortest relaxation time, at the center of the wall. In natural Fe, the relaxation rates vary linearly with temperature over the whole temperature range. This linear temperature variation and the shape of the relaxation curves give independent evidence that the main mode of both longitudinal and transverse relaxation in natural iron is via emission or absorption of single real-bulk magnons. For natural Fe, we find that $\frac{1}{T_{01}T}=22\mathrm{}\pm 2$ ${\mathrm{deg}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ and $\frac{1}{T_{02}T}=28\mathrm{}\pm 3$ ${\mathrm{deg}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$. At 1.2 and 4.2°K, we observe other relaxation mechanisms in a 90.7% enriched ${\mathrm{Fe}}^{57}$ sample. The dominant mechanism here is believed to be a spin-spin interaction of the Suhl-Nakamura type.