A memory element in a cross-bar configuration for reading and writing bits. In order to read a stored bit, a spin-valve structure is used. This structure consists of a soft magnetostrictive layer separated from a permanently magnetized hard magnet by a thin spacer layer. Let us say that the magnetization orientation of the hard magnet represents bit 1. If the soft layer stores bit 1, its magnetization is parallel to that of the hard layer and the vertical resistance of the spin valve structure will be small. If the soft layer stores bit 0, its magnetization is antiparallel to that of the hard layer and the spin-valve’s resistance will be larger. Thus, by reading the spin-valve’s ac resistance with a small signal, we can read the stored bit. The resistance is measured between the upper and lower cross-bars. For writing, the stored bit is first read. If it is the desired bit, no action is taken. Otherwise, the bit is flipped by applying a potential between the upper and lower cross-bars. This potential is dropped mostly across the piezoelectric since the magnets are metallic and the spacer layer is ultrathin.
