Basf Aktiengesellschaft

Georg Schnell

Fritz Hammon

Manfred Ohlinger

Karl-Juergen Reimer

The invention relates to a process for improving the magnetic properties, especially the remanent magnetization, of gamma-iron(III) oxide which can be used advantageously as the magnetic component in magnetic recording media exhibiting reduced print-through. For this purpose, a gamma-iron(III) oxide manufactured according to known processes is heated at temperatures of from 400.degree. to 700.degree. C., the magnetic pigment having basic compounds on the crystal surface during this heat treatment and retaining a pH value above 8 until heating is over. Gamma-iron(III) oxide magnetic pigments treated in this way are particularly suitable for the manufacture of low-noise magnetic recording media with high remanent magnetization and particularly low print-through.

Improving the magnetic properties of gamma-iron (III) oxide

This invention concerns methods and devices for switching a tape-recorder or cassette tape-recorder and especially recorders on which tapes with different magnetic coatings can be used. According to the invention, at least one section along the magnetic tape which has a much higher electric resistance than the magnetic coating is used in conjunction with arrangements of simple layout and in advantageous manner to monitor the resistance of the tape either continuously or sporadically, and at least one predetermined switching state of the recorder is allocated to each different resistance value. This ensures reliable switching of any such states as 'machine on', 'machine off' or 'iron oxide (chromium dioxide) tape' bias, without any other special changes at the magnetic tape or at the cassette.

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Ludwigshafen, Germany

Georg Schnell