  Quantum hydrodynamic (QHD) model of charged spin-1/2 particles contains
physical quantities defined for all particles of a species including particles
with spin-up and with spin-down. Different population of states with different
spin direction is included in the spin density (magnetization). In this paper
we derive a QHD model, which separately describes spin-up electrons and
spin-down electrons. Hence we consider electrons with different projection of
spin on the preferable direction as two different species of particles. We show
that numbers of particles with different spin direction do not conserve. Hence
the continuity equations contain sources of particles. These sources are caused
by the interactions of spins with magnetic field. Terms of similar nature arise
in the Euler equation. We have that z-projection of the spin density is no
longer an independent variable. It is proportional to difference between
concentrations of electrons with spin-up and electrons with spin-down. In terms
of new model we consider propagation of waves in magnetized plasmas of
degenerate electrons and motionless ions. We show that new form of QHD
equations gives all solutions obtained from traditional form of QHD equations
with no distinguish of spin-up and spin-down states. But it also reveals a
sound-like solution we call the spin-electron acoustic wave. Coincidence of
most solutions is expected since we started derivation with the same basic
equation.
