  For a spin-polarized plane wave passing through a spin-rotator containing
uniform magnetic field, we provide a detailed analysis for solving the
appropriate Schr\"{o}dinger equation. A modified expression for spin precession
is obtained which reduces to the standard Larmor precession relation when
kinetic energy is very large compared to the spin-magnetic field interaction.
We show that there are experimentally verifiable regimes of departure from the
standard Larmor precession formula. The treatment is then extended to the case
of a spin-polarized wave packet passing through a uniform magnetic field. The
results based on the standard expression for Larmor precession and that
obtained from the modified formula are compared in various regimes of the
experimental parameters.
