Magnetic structure of the mixed antiferromagnet ${\mathrm{NdMn}}_{0.8}{\mathrm{Fe}}_{0.2}{\mathrm{O}}_3$

The magnetic structure of the mixed antiferromagnet ${\mathrm{NdMn}}_{0.8}{\mathrm{Fe}}_{0.2}{\mathrm{O}}_3$ was resolved. Neutron powder diffraction data definitively resolve the Mn sublattice with a magnetic propagation vector $\mathbf{k}=\left(000\right)$ and with the magnetic structure ($A_x,F_y,G_z$) for 1.6 K $<T<T_{\mathrm{N}}(\approx 59$ K). The Nd sublattice has a ($0,f_y,0$) contribution in the same temperature interval. The Mn sublattice undergoes a spin-reorientation transition at $T_1\approx 13$ K while the Nd magnetic moment abruptly increases at this temperature. Powder x-ray diffraction shows a strong magnetoelastic effect at $T_{\mathrm{N}}$ but no additional structural phase transitions from 3 to 300 K. Density functional theory calculations confirm the magnetic structure of the undoped ${\mathrm{NdMnO}}_3$ as part of our analysis. Taken together, these results show that the magnetic structure of the Mn sublattice in ${\mathrm{NdMn}}_{0.8}{\mathrm{Fe}}_{0.2}{\mathrm{O}}_3$ is a combination of the Mn and Fe parent compounds, but the magnetic ordering of the Nd sublattice spans a broader temperature interval than in the case of ${\mathrm{NdMnO}}_3$ and ${\mathrm{NdFeO}}_3$. This result is a consequence of the fact that the Nd ions do not order independently, but via polarization from the Mn/Fe sublattice.

Figure 1

Determined magnetic structures for (a) ${\mathrm{NdMnO}}_3$ ($T_1\approx 13$ K; $T_{\mathrm{N}}\approx 78$ K) by Muñoz et al. [9]; (b) ${\mathrm{NdMnO}}_3$ ($T_1\approx 20$ K; $T_{\mathrm{N}}\approx 82$ K) by Chatterji et al. [10]; (c) ${\mathrm{NdMn}}_{0.8}{\mathrm{Fe}}_{0.2}{\mathrm{O}}_3$ ($T_1\approx 13$ K; $T_{\mathrm{N}}\approx 59$ K), this work; and (d) ${\mathrm{NdFeO}}_3$ (left panel: $T<10$ K; right panel: $T_1\approx 167$ K; $T_{\mathrm{N}}=690$ K) from other authors [8, 19, 20]. The additional 2D projections of the magnetic structures are presented in Fig. SM1 of Supplemental Material (SM) [33]. This drawing was made using the program vesta [34].

Figure 2

The temperature evolution of the crystallographic parameters as determined by fitting the low-temperature XRPD data using the Le Bail method. Raw data used for the analysis are presented in Fig. SM2 [33].

Figure 3

Temperature variation of the diffraction intensities as a function of $2\theta$ for ${\mathrm{NdMn}}_{0.8}{\mathrm{Fe}}_{0.2}{\mathrm{O}}_3$. The color scale for the observed intensity is given to the right of the main plot of data collected on the E6 diffractometer at HZB.

Figure 4

Temperature variation of the integrated intensities of the (a) overlapping (121), (002), and (210) reflections, and (b) (200) reflection. Data collected on the E6 diffractometer at HZB.

Figure 5

The temperature evolution of the magnetic components and absolute value of the Mn magnetic moment for the magnetic structure (a) ${\mathrm{\Gamma }}_{5\mathrm{Mn}}{\mathrm{\Gamma }}_{5\mathrm{Nd}}$ and (b) ${\mathrm{\Gamma }}_{5\mathrm{Mn}}{\mathrm{\Gamma }}_{0\mathrm{Nd}}$. The solid lines represent the best fits according to Eq. (3).

Figure 6

The NPD patterns obtained, after subtracting a linear background, in the vicinity of the (110) and (011) reflections as measured on the HB-3 triple-axis instrument at ORNL. The lines represent Gaussian fits of the intensity.