Multimodal media for magnetic recording

Using mixtures of Co-Fe-Ni alloy particles with different coercivity populations, or mixtures of the alloy particles with other particulate ferro- or ferri-magnetic materials (also of differing coercivities), we have made magnetic recording media with little magnetic interaction between the two or more particle populations. Average coercivities of these separate particle populations need only be 200 Oe apart in order that "multimodal" action is achieved. Such multimodal media are characterized by successive pseudomajor hysteresis loops, which expand stepwise with the maximum applied field. Such recording media can contain as many sets of signals as the number of modes, the sets being eraseable in sequence independently of higher mode signals. Uses of such media include masking of a wanted signal recorded in a higher mode with another (meaningless) signal recorded in a lower mode, or the dubbing of editing information (which can later be erased). Since the mixing of iron or chromium oxide particles of widely differing coercivities does not generally yield a multimodal medium, the magnetic interaction in our systems is undoubtedly not the same as in the oxide systems.