We report magnetic susceptibility and electrical resistivity measurements under hydrostatic pressure up to 2 GPa on single-crystalline $\mathrm{Pr}{\mathrm{Cu}}_2$, which exhibits the pressure-induced Van Vleck paramagnet-to-antiferromagnet transition at 1.2 GPa. The measured anisotropy in the susceptibility shows that the ordered $4f$ moments lie in the ac plane in the pressure-induced magnetic state. We propose that remarkable pressure effects on the susceptibility and resistivity are due to changes in the quadrupolar state of $O_2^2$ and/or $O_2^0$ under pressure. We present a simple analysis in terms of the singlet-singlet model.

• Received 20 July 2004

DOI:https://doi.org/10.1103/PhysRevB.71.024408