These are the magnets on the left side of the iPad 2 -- the ones that attract the Smart Cover's frame. They're integrated into the iPad 2's back cover, and held in place with four #00 Phillips screws.
These magnets form the same rounded contour as the exterior of the iPad 2's aluminum case. This allows for the best possible connection between the magnets in the iPad 2 and those in the Smart Cover's frame.
Interestingly, these magnets' polarities were manually marked -- a blue dash written with a marker -- instead of having a machine stamp/engrave the polarity into them.