  We study phase transitions in heavy fermion systems due to spin-wave
instabilities. One motivation is to determine the changes in the spin-wave
parameters of a magnetically ordered heavy fermion system as it approaches a
quantum critical point (QCP) by applying pressure. The other more actual is to
provide an alternative approach, based on spin-wave instabilities, for the
magnetic field induced transitions recently observed in antiferromagnetic heavy
fermion materials.
