  The heavy fermion antiferromagnet CeNiGe2 was investigated under pressure by
resistivity and ac calorimetry up to 4 GPa and down to 40 mK. The two magnetic
transitions found in both resistivity and specific heat at 0.1 GPa at T_N1=3.95
and T_{N2}=3.21 K are replaced by a single one at 0.7 GPa and 2.81 K.
Increasing pressure initially reduces this further, however at about 1.7 GPa a
new transition appears, accompanied by a marked change in the pressure
dependence of the ordering temperatures, the temperature dependence of the
resistivity, and the residual resistivity. There are signs that this new
transition has some first order character. The phase diagram of CeNiGe2 bears
little resemblance to the Doniach phase diagram widely used to classify heavy
fermion compounds.
