Switching properties of multilayer nickel-iron films with a ferrite keeper

The threshold currents necessary for writing and those leading to a destruction of the stored information are determined for 0.4-mm by 0.8-mm elements of single and multilayer films of different thicknesses, without and with a ferrite keeper. The multilayer films consist of two nickel-iron films coupled through a very thin film of a nonmagnetic metal, for instance, gold. A test program with 2.10⁴pulses for alternatingly writing zero and one, or with 2.10⁴disturb pulses, respectively, is used. For making the keeper-to-film separation as small as possible, the drive lines are evaporated onto the two surfaces of one 6-mμ-thick Mylar foil. The results show that the acceptable film thickness, yielding sufficiently large tolerances for the drive currents in a word-organized DRO memory, is increased by the factor 1.7 to 1.8, by using multilayer films instead of single films, as well as a sintered ferrite keeper, which yields a factor of 3 for the combination of both.