Changes in pressure and magnetic field in the orbital and magnetic ordering temperatures of $R{\mathrm{VO}}_3$ perovskites are reported; they reveal a competition between two magnetic orbitally ordered phases that have opposite preferences for the $e$-orbital component in the localized ${}^{3}T_{1g}$ ground state of the ${\mathrm{V}}^{3+}$ ion. This competition is shown to be biased by the ${\mathrm{VO}}_{6/2}$ site distortion intrinsic to the orthorhombic structure. A remarkable enhancement of $T_N$ with pressure is found where the competition leads to enhanced orbital critical fluctuations.

• Received 18 May 2007

DOI:https://doi.org/10.1103/PhysRevLett.99.156401