Improved flat Ni-Fe-film elements obtained by diffusion of an electroplated nonmagnetic layer

The storage properties of flat thin Ni-Fe films can be improved by diffusing a nonmagnetic metal into them. Usually this metal is deposited on the Ni-Fe film in a vacuum chamber. By this well-known technique one can also electroplate the non-magnetic overlay. Several metals, e.g., Zn, Cd, Cu, Pb, Sn, Bi, and In have been tried. Tin gave the best reproducibility. The dispersion remains almost unchanged up to a ratio of 1, so that very good bit current margins are achieved. To avoid demagnetization effects, which could mask the film qualities, large spots were investigated. It was found that the creep threshold is independent of the film thickness (350-1000 Å). An explanation for this desirable behavior can be found if one assumes that the nonmagnetic metal fills up and enlarges easy-diffusion paths in the film and thus creates obstacles for a creeping wall. Despite the low diffusion temperature for Sn, 50-100°C, the long-time stability of the magnetic parameters is good, and it is possible to get uniform magnetic parameters on large memory planes.