  Spintronics logic devices based on majority gates formed by atomic-level
arrangements of spins in the crystal lattice is considered. The dynamics of
switching is modeled by time-dependent solution of the density-matrix equation
with relaxation. The devices are shown to satisfy requirements for logic.
Switching speed and dissipated energy are calculated and compared with
electronic transistors. The simulations show that for the highly idealized case
assumed here, it is possible to trade off size for speed and achieve lower
power operation than ultimately scaled CMOS devices.
