The spin-torque effect in a nanomagnet. (top left) If the
polarization of the spins in the current (, green arrow) is
parallel to the easy axis (black arrow), the spin torque opposes
the natural damping and opens up the angle of the precession
cone at all points along the cone. (top right) If makes a finite
angle with the easy axis, the spin torque opens the precession
cone angle around a half circle centered at point , but closes
the cone angle in the other half circle centered at point .
Applying two successive spin-torque pulses either both at point
, or at points and , increases or decreases the net
effectiveness of the spin torque in inducing a dynamic switch.
(bottom) Schematic of the nanopillar structure. The free layer
is the right layer and the current is applied along the
horizontal axis of the pillar. The polarization of the current
(green arrows) also rotates as a result of the spin-torque
effect.