Structural transformation and magnetic competition inYb(Mn1−xFex)O

Structural and magnetic properties of the $\mathrm{Yb}({\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}){\mathrm{O}}_{3}$ $(0\ensuremath{\leqslant}x\ensuremath{\leqslant}1)$ system have been systematically investigated. Initial samples were prepared via a sol-gel method. A pure hexagonal phase was only obtained for samples with $x\ensuremath{\leqslant}0.5$. With high-pressure annealing, a pure orthorhombic perovskite phase was achieved for all the compositions. The $^{57}\mathrm{Fe}$ M\"ossbauer spectrum for $x=0.5$ shows that only ${\mathrm{Fe}}^{3+}$ ions exist in the system; there was no evidence of chemical inhomogeneities. With increasing $x$, the N\'eel temperature ${T}_{N}$ increases for both hexagonal and orthorhombic phases. The orthorhombic $\mathrm{Yb}({\mathrm{Mn}}_{0.5}{\mathrm{Fe}}_{0.5}){\mathrm{O}}_{3}$ shows an interesting weak ferromagnetic state in the temperature range of $239--298\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the ferromagnetism disappearing abruptly on cooling below ${T}_{t}=239\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The transition at ${T}_{t}$ appears to be a reorientation of the spin axis of a type-$G$ antiferromagnetic order from the orthorhombic $a$ axis to the $b$ axis in the (010) plane.