Thin permalloy films: optimization of properties for computer memories

The vacuum deposition of Ni-Fe elements on glass for use in a 6000 bit, 100 ns cycle time memory is described. Measurement of the magnetic properties of some 20 000 elements has enabled reliable correlation to be made with film composition and deposition conditions. Memory testing of elements made with calculated optimum dimensions show that films 100 nm thick have wide operating limits because of high coercivity and freedom from cross-tie walls. Tapering the ends of the elements increased the domain nucleation coercivity above the wall coercivity. Although producing films with rectangular hysteresis loops, tapering did not increase the creep disturbance threshold. Films thicker than 180 nm show anomalous domain configurations in hard direction fields together with a steep rise in wall coercivity and increased dispersion.