Proposal for Magnetic Domain-Wall Storage and Logic

Abstract

Magnetic storage of binary digital information is currently accomplished by utilizing the two stable and degenerate energy states corresponding to opposite spatial directions of a magnetic domain. However, a second type of magnetic-energy degeneracy exists since a domain wall separating two domains has the same energy regardless of the sense (clockwise or counter-clockwise) of rotation of the magnetization M within the wall. Hence, the rotational sense of M in passing through a wall can be used to represent binary information. The two methods of representation are essentially different since different aspects of spatial symmetry are involved. A practical method of utilizing wall-rotation information coding can be effected by means of strips of thin magnetic film and nearby current conductors which are used to generate magnetic fields in specified directions at specified times and places. A shift register consists of a regular up-and-down domain pattern with M perpendicular to the long strip axis; no information is contained in the domain pattern itself, which only serves to separate spatially the information-bearing walls. Shifting is accomplished by two-phase clock pulses on a pair of shifting windings. Read-out requires the use of the operation of conditional erase, accomplished as follows: if two walls of the same sense are brought together they form a double wall which can subsequently be separated into two walls; if the walls are of the opposite sense they will destroy one another upon being brought together. Thus, erasure occurs on condition that two walls have opposite sense.