Abstract: A ferrimagnetic medium is locally heated above its compensation temperature and a magnetic record head provides a magnetic field for data recording on the heated portion of the medium. Upon re-cooling to the compensation temperature, the recorded signal is magnetically "locked" in the medium. The user of a magnetic head to provide the recording magnetic field allows fast head current switching rates with attendant high density data recording or high speed erasure of the medium. The recorded medium is read by means of conventional magneto-optic apparatus.