An apparatus for selectively inverting an external magnetic field in a magneto-optic recording system so that information can be selectively recorded on or erased from a magneto-optic recording element of the system moving through said field, the apparatus comprises a permanent magnet having its north and south poles oriented along its cross-sectional dimension. A core having a shape which is adaptable to selectively impart a predetermined magnetic field to the permanent magnet for rotating the permanent magnet, which directs a flux generated by the predetermined magnetic field for reducing electro-magnetic interference, and which defines a preferential orientation of the magnet for selectively maintaining the magnet in the preferential orientation.