Magnetic structure of ${\mathrm{TbMnO}}_3$ by 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.

Figure 1

(Color online) Neutron diffraction profiles along (a) the $(0,k,0)$ line and (b) the $(0,k,1)$ line at 4, 10, and $55\mathrm{K}$. Vertical lines indicate the positions of the $\mathrm{Mn}$ ($k\approx \text{integer}\pm 2∕7$ and $6∕7$) and $\mathrm{Tb}$ ($k\approx \text{integer}\pm 3∕7$ and $6∕7$) superlattice peaks. $“\mathrm{Al}”$ denotes diffractions from the aluminum sample cell.

Figure 2

(a)–(d) Temperature dependences of the intensities of the $\mathrm{Mn}$ superlattice peaks of (a) $A$ type, (b) $G$ type, (c) $F$ type, and (d) $C$ type. (e) Temperature dependence of the intensity of the $\mathrm{Mn}$ third harmonics at $(0,0.835,1)=(0,3q_{\mathrm{Mn}},1)$.

Figure 3

Temperature dependences of the peak intensities due to the $\mathrm{Tb}$ ordering at (a) $(0,0.424,1)=(0,q_{\mathrm{Tb}},1)$ and (b) $(0,1.151,2)=(0,2-2q_{\mathrm{Tb}},2)$.

Figure 4

Temperature dependences of (a) the peak intensity, (b) the wave number, and (c) the peak width of the $\mathrm{Mn}$ $(0,q_{\mathrm{Mn}},1)$ peak. Inset of panel (a): Temperature dependence of the $\mathrm{Mn}$ peak profile at $(0,q_{\mathrm{Mn}},1)$ along the [010] direction.