Characteristics of Bloch-Line Pair Propagation Using Film Thickness Modulation (FTM) Patterns for Bit Confinement

A new bit confinement method for Bloch-line (BL) memories which uses film thickness modulation (FTM) has been studied, as a means of making the BL pair propagation common to both sides of the stripe domain wall. Since it is necessary to make the modulation pattern edge smooth for propagation under low driving fields, we used tapered resist patterns for the ion milling mask and carried out the milling to produce a modulation of amplitude 100 nm in an O2 atmosphere (10^¿6 Torr). BL pair propagation was tested using a sawtooth pulsed bias field with a 100 ns rise time and a 1000 ns fall time. It was found that the driving field margins did not depend on the propagation direction, because the bit confinement force acts symmetrically on both sides of the domain wall. Furthermore, it was confirmed that the temperature dependence of the driving field margin is larger than that when using the conventional magnetic pattern method.