  We investigate the dependence of perpendicular and parallel spin transfer
torque (STT) and tunneling magnetoresistance (TMR) on the insulator barrier
energy in the magnetic tunnel junction (MTJ). We employed single orbit tight
binding model combined with the Keldysh non-equilibrium Green's function method
in order to calculate the perpendicular and parallel STT, and TMR in MTJ with
the finite bias voltages. The dependences of STT and TMR on the insulator
barrier energy are calculated for the semi-infinite half metallic ferromagnetic
electrodes. We find that perfect linear relation between the parallel STT and
the tunneling current for the wide range of the insulator barrier energy.
Furthermore, the TMR also depends on the insulator barrier energy, which
contradicts to the Julliere's simple model.
