Observation of C -type orbital ordered phase and orbital flipping in LaVO3

The orthovanadate system $R\mathrm{V}{\mathrm{O}}_{3}$ ($R=\mathrm{rare}$-earth and Y) is known to exhibit multiple orbital, magnetic, and structural transitions depending on the size of the rare-earth ions. $\mathrm{LaV}{\mathrm{O}}_{3}$ is reported to exhibit a $G$-type orbital ordered ($G$-OO) phase and magnetization reversal below the antiferromagnetic transition. From high angular-resolution synchrotron x-ray powder diffraction measurements, we report the observation of the $C$-OO phase, hitherto unknown in $\mathrm{LaV}{\mathrm{O}}_{3}$, and its coexistence with the $G$-OO phase below ${T}_{\mathrm{OO}}^{1}$ ($\ensuremath{\sim}135$ and 125 K) in ambient-pressure (AP) and high-pressure (HP) synthesized $\mathrm{LaV}{\mathrm{O}}_{3}$, respectively. At ${T}_{\mathrm{OO}}^{2}\ensuremath{\sim}20$ K, HP-$\mathrm{LaV}{\mathrm{O}}_{3}$ shows an orbital flipping transition from $G$- to $C$-OO, which results in an increase of the $C$-OO phase fraction. At 6 K, the $C$-OO phase becomes predominant ($\ensuremath{\sim}61%$) in HP-$\mathrm{LaV}{\mathrm{O}}_{3}$, whereas it is $\ensuremath{\sim}41%$ in AP-$\mathrm{LaV}{\mathrm{O}}_{3}$. We suggest that the different magnetic structures associated with coexisting orbital ordered phases should be responsible for the magnetization reversal phenomenon in $\mathrm{LaV}{\mathrm{O}}_{3}$.