  Magnetoresistivity $\rho _{xx}$ and $\rho _{xy}$ and the acoustoelectronic
effects are measured in $p$-Si/SiGe/Si with an impurity concentration $p$ = 2
$\times $ 10$^{11}$ cm$^{-2}$ in the temperature range 0.3-2.0 K and an tilted
magnetic field up to 18 T. The dependence of the effective $g$-factor on the
angle of magnetic field tilt $\theta $ to the normal to the plane of a two
dimensional $p$-Si/SiGe/Si channel is determined. A first order
ferromagnet-paramagnet phase transition is observed in the magnetic fields
corresponding to a filling factor $\nu $ = 2 at $\theta \approx $
59$^\textrm{o}$-60$^\textrm{o}$.
