Magnetic Order in the Heavy Fermion CompoundCeCu6at mK Temperatures

We have measured the ac magnetic susceptibility in various fields and thermal expansion of single crystals of the heavy fermion compound ${\mathrm{CeCu}}_{6}$ at temperatures down to $250\ensuremath{\mu}\mathrm{K}$. The susceptibility of ${\mathrm{CeCu}}_{6}$ shows a peak at about 2 mK and has a large anisotropy. We also detected an anomaly of thermal expansion at the same temperature. The observed behaviors of the susceptibility and the thermal expansion in ${\mathrm{CeCu}}_{6}$ indicate the occurrence of an antiferromagnetic order.