  The interplay of magnetic and superconducting fluctuations in two dimensional
systems with van Hove singularities in the electronic spectrum is considered
within the functional renormalization group (fRG) approach. While the fRG flow
has to be stoped at a certain minimal temperature T_RG^min, we study
temperature dependence of magnetic and superconducting susceptibilities both,
above and below T_RG^min, which allows to obtain the resulting ground state
phase diagram. Close to half filling the fRG approach yields two quantum phase
transitions: from commensurate antiferromagnetic to incommensurate phase and
from the incommensurate to paramagnetic phase, the region of the commensurate
magnetic phase is possibly phase separated away from half filling. Similarly to
results of Hertz-Moriya-Millis approach, the temperature dependence of the
inverse (incommensurate) magnetic susceptibility at the quantum phase
transition from incommensurate to paramagnetic phase is found almost linear in
temperature.
