The angular momentum compensation temperature $T_{ \rm A}$ of ferrimagnets has attracted much attention because of high-speed magnetic dynamics near $T_{ \rm A}$. We show that NMR can be used to investigate domain wall dynamics near $T_{ \rm A}$ in ferrimagnets. We performed $^{ 57}$Fe-NMR measurements on the ferrimagnet Ho$_3$Fe$_5$O$_{ 12}$ with $T_{ \rm A} = 245$ K. In a multi-domain state, the NMR signal is enhanced by domain wall motion. We found that the NMR signal enhancement shows a maximum at $T_{ \rm A}$ in the multi-domain state. The NMR signal enhancement occurs due to increasing domain-wall mobility toward $T_{ \rm A}$. We develop the NMR signal enhancement model involves domain-wall mobility. Our study shows that NMR in multi-domain state is a powerful tool to determine $T_{ \rm A}$, even from a powder sample and it expands the possibility of searching for angular momentum-compensated materials.
Categories: cond-mat.mtrl-sci