Reduction of switching field in spin-flop switching for high-density magnetic random access memory

A magnetization switching method for magnetic random access memory (MRAM), recently proposed by Savtchenko et al. [U.S. Patent No. 6,545,906 (2003)], is known to have an important advantage of a wide window for bit writing over the conventional method based on the asteroid curve, but it has a serious problem of high switching fields. In an effort to solve this problem, the effects of the thickness asymmetry and antiferromagnetic exchange coupling of the synthetic antiferromagnetic free-layer structure on the switching field have been investigated by micromagnetic computer simulation. At conditions relevant to high-density MRAM, magnetization switching in the direct write mode occurs at reasonably low values of word- and bit-line fields (below 100 Oe), combined with a substantially wide window for bit writing. A much wider window is observed in the toggle mode, but the required switching fields are too high, being over 150 Oe.