${\mathrm{Fe}}^{57}$ Nuclear Magnetic Resonance and Some Dynamical Characteristics of Domain Walls in $\alpha -{\mathrm{Fe}}_2{\mathrm{O}}_3$

Steady-state ${\mathrm{Fe}}^{57}$ nuclear magnetic resonance (NMR) signals in $\alpha -{\mathrm{Fe}}_2{\mathrm{O}}_3$ have been re-examined using large good-quality synthetic single crystals. It has been confirmed that strong signals originate in domain walls. The detected signal is related to the electronic loss modulated by the real part of the susceptibility of the nuclear spins, ${\chi }_n^{\prime }$. The total loss detected in a coil is proportional to $1+m{\chi }_n^{\prime }$, where $m$ is the modulation index. It is shown theoretically that for a domain wall with a wall resonance frequency ${\nu }_0>{\nu }_N$, where ${\nu }_N$ is the NMR frequency, $m$ is positive; while for a wall with ${\nu }_0<{\nu }_N$, $m$ is negative. This effect has been observed experimentally and correlated with domain-pattern observations, magnetization measurements, and also pulsed-NMR experimental results.