  The relation between tunnel magneto-resistance (TMR) and spin polarization is
explored for GaMnAs/GaAlAs/GaMnAs structures where the carriers experience
strong spin-orbit interactions. TMR is calculated using Landauer approach. The
materials are described in the 6 band $\bf {k}\cdot \bf{p}$ model which
includes spin orbit interaction. Ferromagnetism is described in the virtual
crystal mean field approximations. Our results indicate that TMR is a function
of of spin polarization and barrier thickness. As a result of the stong spin
orbit interactions, TMR also depends on the the angle between current flow
direction and the electrode magnetization. These results compromise the
validity of Julliere formula.
