Ordered magnetic and quadrupolar states under hydrostatic pressure in   orthorhombic PrCu2
  We report magnetic susceptibility and electrical resistivity measurements on single-crystalline PrCu2 under hydrostatic pressure, up to 2 GPa, which pressure range covers the pressure-induced Van Vleck paramagnet-to-antiferromagnet transition at 1.2 GPa. The measured anisotropy in the susceptibility shows that in the pressure-induced magnetic state the ordered 4f-moments lie in the ac-plane. We propose that remarkable pressure effects on the susceptibility and resistivity are due to changes in the quadrupolar state of O22 and/or O20 under pressure. We present a simple analysis in terms of the singlet-singlet model. 
T. Naka, L. A. Ponomarenko, A. de Visser, A. Matsushita, R. Settai and   Y. Onuki