We have measured the electrical resistivity through the magnetic phase transition of the nuclear spins in the Van Vleck paramagnet ${\mathrm{PrCu}}_6$ with varying frequencies and applied magnetic fields. The electrical resistivity starts to decrease at the transition temperature ${\mathit{T}}_{\mathit{c}}$ and becomes constant well below ${\mathit{T}}_{\mathit{c}}$. This resistivity decrease is found to be caused by the ferromagnetic alignment of the nuclear spins. We have also observed a critical phenomenon just above ${\mathit{T}}_{\mathit{c}}$. This critical phenomenon can be explained by a simple calculation.

• Received 2 April 1992

DOI:https://doi.org/10.1103/PhysRevLett.69.375