Magnetic order in the heavy fermion compound CeCu₆ at mK temperatures

We have measured the ac magnetic susceptibility in various fields and thermal expansion of single crystals of the heavy fermion compound CeCu₆ at temperatures down to 250 μK. The susceptibility of CeCu₆ 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 CeCu₆ indicate the occurrence of an antiferromagnetic order.