Electromagnetic field is really complicated. However, when a magnet is moved, it produces an electromagnetic field. If you place a wire near that field, it will induce charge in the wire. The amount of charge/induction depends on many factors such as orientation of the magnet/field relative to the wire, size of the magnet, speed of magnet rotation, thickness of wire, distance, etc....
You could just be inducing voltage/charge in your measuring wires by holding them close to your magnet.
http://en.wikipedia.org/wiki/Magnetic_field
