Magnetic order in ${\text{YbMnO}}_3$ studied by neutron diffraction and Mössbauer spectroscopy

The magnetic ordering of the hexagonal multiferroic compound ${\text{YbMnO}}_3$ has been studied between 100 and 1.5 K by combining neutron powder diffraction, ${}^{170}\text{Y}\text{b}$ Mössbauer spectroscopy, and magnetization measurements. The Yb moments of the two crystallographic sites order at two different temperatures: the $4b$ site together with the Mn moments (at $T_N\simeq 85\text{K}$) and the $2a$ site well below (at 3.5 K). The temperature dependences of the Mn and Yb moments are explained within a molecular-field model, showing that the $4b$ and $2a$ sites order via Yb-Mn and Yb-Yb interactions, respectively. A simple picture taking into account the local Mn environment of the rare-earth $R$ $\left(4b\right)$ ion is proposed to couple $R$ and Mn orders in hexagonal $R{\text{MnO}}_3$ manganites. The nature and symmetry of the $R\text{-Mn}$ interactions yielding the $R$ order are discussed.

Figure 1

(Color online) Observed and FULLPROF calculated NPD pattern at room temperature. The Bragg reflections (ticks) and the difference between the observed and calculated patterns are plotted at the bottom.

Figure 2

(Color online) Inverse magnetic susceptibility in ${\text{YbMnO}}_3$. The dashed line is a Curie-Weiss law with ${\mu }_{\text{eff}}=6.1{\mu }_B$ and ${\theta }_p=-220\text{K}$. Inset: low-temperature susceptibility.

Figure 3

(Color online) ${}^{170}\text{Y}\text{b}$ Mössbauer spectra in ${\text{YbMnO}}_3$ at selected temperatures. The subspectrum corresponding to the minority $\text{Yb}\left(2a\right)$ site (relative occupancy 1/3) is drawn in red and that corresponding to the $\text{Yb}\left(4b\right)$ site in blue.

Figure 4

(Color online) Thermal variation in the ${\text{Yb}}^{3+}\left(2a\right)$ relaxation rate extracted from the ${}^{170}\text{Y}\text{b}$ Mössbauer spectra in ${\text{YbMnO}}_3$. The dashed line is a guide for the eyes and the red arrow marks the (probably) ferromagnetic transition of the $\text{Yb}\left(2a\right)$ sites.

Figure 5

(Color online) Observed and FULLPROF calculated NPD patterns between 1.5 and 100 K. The Bragg reflections (ticks) and the difference between the observed and calculated patterns are plotted at the bottom.

Figure 6

(Color online) Integrated intensities of the (100), (101), and (102) reflections between 1.5 and 100 K (lines are guides for the eyes).

Figure 7

(Color online) Symmetry allowed Mn spin orders in hexagonal $R{\text{MnO}}_3$. In ${\text{YbMnO}}_3$, ${\Gamma }_2$ or ${\Gamma }_4$ IR yield the best fit to experiment.

Figure 8

(Color online) Observed Mn, $\text{Yb}\left(4b\right)$, and $\text{Yb}\left(2a\right)$ moments from NPD and Mössbauer measurements (dots) versus temperature. The solid lines correspond to the molecular-field calculation.