  We investigate linear and non-linear transport in a double quantum dot system
weakly coupled to spin-polarized leads.
  In the linear regime, the conductance as well as the non-equilibrium spin
accumulation are evaluated in analytic form. The conductance as a function of
the gate voltage exhibits four peaks of different height, with mirror symmetry
with respect to the charge neutrality point. As the polarization angle is
varied, the position and shape of the peaks changes in a characteristic way
which preserves the electron-hole symmetry of the problem. In the nonlinear
regime negative differential conductance features occur for non collinear
magnetisations of the leads. In the considered sequential tunneling limit, the
tunneling magneto resistance (TMR) is always positive with a characteristic
gate voltage dependence for non-collinear magnetization. If a magnetic field is
added to the system, the TMR can become negative.
