  We address spin polarization dependence of graphene's Fermi liquid properties
quantitatively using a microscopic Random Phase Approximation theory in an
interacting spin-polarized Dirac electron system. We show an enhancement of the
minority-spin many-body velocity renormalization at fully spin polarization due
to reduction in the electron density and consequently increase in the
interaction between electrons near the Fermi surface. We also show that the
spin dependence of the Fermi velocity in the chiral Fermi systems is different
than that in a conventional two-dimensional electron liquid. In addition, we
show that the ratio of the majority- to minority-spin lifetime is smaller than
unity and related directly to the polarization and electron energy. The
spin-polarization dependence of the carrier Fermi velocity is of significance
in various spintronic applications.
