Exchange coupled MO films like (PtCo/TbFeCo) and TbFeCo/TbFeCo) enable a very small external field of only 50 Oe for erase and write. Those are suitable media for a field modulation overwriting. In plane magnetized PtCo or low perpendicular anisotropy TbFeCo acts as the external field enhancing layer through exchange coupling with the TbFeCo recording layer.