  Mechanisms of 'environmental decoherence' such as surface scattering,
Elliot-Yafet process and precession mechanisms, as well as their influence on
the spin phase relaxation are considered and compared. It is shown that the
'spin ballistic' regime is possible, when the phase relaxation length for the
spin part of the wave function (WF)is much greater than the phase relaxation
length for the 'orbital part'. In the presence of an additional magnetic field,
the spin part of the electron's WF acquires a phase shift due to additional
spin precession about that field. If the structure length is chosen to be
greater than the phase relaxation length for the 'orbital part' and less than
the phase relaxation length for the spin part of WF, it is possible to 'wash
out' the quantum interference related to the phase coherence of the 'orbital
part' of the WF, retaining at the same time that related to the phase coherence
of the spin part and, hence, to reveal corresponding conductance oscillations.
