Structural transformation and magnetic competition in $\mathrm{Yb}\left({\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\right){\mathrm{O}}_3$

Structural and magnetic properties of the $\mathrm{Yb}\left({\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\right){\mathrm{O}}_3$ $(0⩽x⩽1)$ system have been systematically investigated. Initial samples were prepared via a sol-gel method. A pure hexagonal phase was only obtained for samples with $x⩽0.5$. With high-pressure annealing, a pure orthorhombic perovskite phase was achieved for all the compositions. The ${}^{57}\mathrm{Fe}$ Mössbauer 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 Néel temperature $T_N$ increases for both hexagonal and orthorhombic phases. The orthorhombic $\mathrm{Yb}\left({\mathrm{Mn}}_{0.5}{\mathrm{Fe}}_{0.5}\right){\mathrm{O}}_3$ shows an interesting weak ferromagnetic state in the temperature range of $239–298\mathrm{K}$, the ferromagnetism disappearing abruptly on cooling below $T_t=239\mathrm{K}$. 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.

Figure 1

XRD patterns for $\mathrm{Yb}\left({\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\right){\mathrm{O}}_3$ with $x=0$, 0.1, 0.3, 0.5, 0.7, and 1.0: (a) sintered at $1200°\mathrm{C}$ for $20\mathrm{h}$ in air, and (b) further annealed at $1100°\mathrm{C}$ for $30\min$ under a pressure of $5\mathrm{GPa}$.

Figure 2

Lattice parameters for (a) hexagonal and (b) orthorhombic $\mathrm{Yb}\left({\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\right){\mathrm{O}}_3$ samples.

Figure 3

(Color online)${}^{57}\mathrm{Fe}$ Mössbauer spectrum at $350\mathrm{K}$ for the orthorhombic $\mathrm{Yb}\left({\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\right){\mathrm{O}}_3$, fitted with two components with essentially identical isomer-shift values of $0.32\text{and}0.33\mathrm{mm}∕\mathrm{s}$.

Figure 4

(Color online) Temperature dependence of zero-field-cooled (ZFC) and field-cooled (FC) susceptibility $\left(\chi \right)$ measured under a field of $100\mathrm{Oe}$ for $\mathrm{Yb}\left({\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\right){\mathrm{O}}_3$ with $x=0–1.0$ (Hex: hexagonal phase without HP annealing; Mix: mixed hexagonal and orthorhombic phases without HP annealing; and Orth: orthorhombic phase obtained via HP annealing).

Figure 5

$d\chi ∕dT$ as a function of temperature for (a) and (b) hexagonal and (c) and (d) orthorhombic $\mathrm{Yb}\left({\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\right){\mathrm{O}}_3$ with $x=0–1.0$.

Figure 6

(Color online) Field-dependent magnetization for the orthorhombic $\mathrm{Yb}\left({\mathrm{Mn}}_{0.5}{\mathrm{Fe}}_{0.5}\right){\mathrm{O}}_3$ at different temperatures; the inset A shows the magnetic hysteresis loop at $250\mathrm{K}$, and the inset B shows the hysteresis loop obtained by subtraction of the paramagnetic component of ${\mathrm{Yb}}^{3+}$ ions.