Almost-localized electrons in a magnetic field.

Within a Gutzwiller type of approach to correlated electrons, the effective mass of quasiparticles composing an almost-localized Fermi liquid is spin dependent and varies strongly with magnetic field. The magnetization of such a system saturates in physically accessible fields. The results are used to explain the field dependence of both the effective mass and of the specific heat in the heavy-fermion systems at low temperature