Spin-split masses and metamagnetic behavior of almost-localized fermions.

We discuss specific features of quasiparticles in a strong applied magnetic field and near the Mott-Hubbard localization: the strong spin dependence of the de Haas--van Alphen oscillations, the maximum in the field dependence of the linear specific-heat coefficient, and metamagnetic behavior. These properties are obtained within the approach involving auxiliary (slave boson) fields that provides both the Gutzwiller band narrowing and a nonlinear molecular field. The simultaneous observation of all three properties provides a consistent set of predictions of the mean-field approach to the almost-localized Fermi liquid. The situation for heavy fermion system CeRu{sub 2}Si{sub 2} is briefly discussed.