A non-erasable magnetic memory based on the magnetic permeability

A non-erasable memory based on using differences in the magnetic permeability is demonstrated. The method can potentially store information indefinitely. Initially the high permeability bits were 10-50 μm wide lines of sputtered permalloy (Ni81Fe19) on a glass substrate. In a second writing technique a continuous film of amorphous, high permeability ferromagnetic Metglas (Fe78Si13B9) was sputtered onto a similar glass substrate. Low permeability, crystalline 50 μm wide lines were then written in the film by laser heating. Both types of written media were read by applying an external probe field that is locally modified by the permeability of each bit. The modifications in the probe field were read by a nearby set of 10 micron wide magnetic tunnel junctions with a signal-to-noise ratio of up to 45 dB. This large response to changes in bit permeability is not altered after the media has been exposed to a 6400 Oe field. While being immediately applicable for data archiving and secure information storage, higher densities are possible with smaller read and write heads.