Magnetic structure ofTbMnO3by neutron diffraction

Magnetic ordering in ${\mathrm{TbMnO}}_3$ was revisited by a neutron diffraction study. In addition to the previously reported $A$-type and $G$-type modulated structures with a propagation vector $(0,q_{\mathrm{Mn}},0)$, we found $C$-type and $F$-type orderings of the $\mathrm{Mn}$ moments. All the components appear below $T_N^{\mathrm{Mn}}=46\mathrm{K}$, and the $G$-, $C$-, and $F$-type components are enhanced below $T_{\text{lock}}=28\mathrm{K}$, where $q_{\mathrm{Mn}}$ ordering locks at its low temperature value. The locking of the propagation vector also yields the squaring up of the spin arrangement. The magnetic moments of $\mathrm{Tb}$ ions show a quasi-long-range ordering below $T_N^{\mathrm{Tb}}=7\mathrm{K}$. It drastically promotes the development of the $G$-, $C$-, and $F$-type components while suppressing the $A$-type components.