  A simple tight-binding theoretical model is proposed for spin dependent,
current-in-plane transport in highly coherent spin valve structures under
specularity conditions. Using quantum-mechanically coherent and spatially
quantized Fermi states in the considered multilayered system, a system of
partial Boltzmann kinetic equations is built for relevant subbands to yield the
expressions for conductance in parallel or antiparallel spin valve states and
thus for the magneto-conductance. It is shown that specularity favors the
magnetoresistance to reach its theoretical maximum for this structure close to
100%. This result is practically independent of the model parameters, in
particular it does not even need that lifetimes of majority and minority
carriers be different (as necessary for the quasiclassical regimes). The main
MR effect in the considered limit is due to the transformation of coherent
quantum states, induced by the relative rotation of magnetization in the FM
layers. Numerical calculation based on the specific Boltzmann equation with an
account of spin-dependent specular reflection at the interfaces is also
performed for a typical choice of material parameters.
