  The dynamics of a single spin embedded in the tunnel junction (quantum point
contact) between ferromagnets is addressed. Using the Keldysh technique, we
derive a quantum Langevin equation. As a consequence of the spin-polarization
in the leads, the spin displays a rich and unusual dynamics. Parallel
configured and equally strong magnetic moments in the leads yield an ordinary
spin precession with a Larmor frequency given by the effective magnetic field.
Unequal and/or non-parallel configured magnetization, however, causes nutation
of the spin in addition to the precession. Our predictions may be directly
tested for macroscopic spin clusters.
