Analysis for toggling magnetic random access memories with low writing field using four ferromagnetic layers for free layer stack

作者：Suzuki T^*; Fukumoto Y; Ishiwata N

来源：Journal of Applied Physics, 2007, 101(2): 023906.

DOI：10.1063/1.2424408

We calculate writing characteristics of two kinds of low-current magnetic random access memory (MRAM) devices using a single domain model. A four-layer synthetic antiferromagnet (SAF) has four antiferromagnetically coupled ferromagnetic (FM) layers, and a two-SM-layer-FC SAF has a two-FM-layer SAF with ferromagnetically coupled (FC) two soft magnetic (SM) layers. The threshold field of these free layers can be calculated analytically. The spin flop field of four-FM-layer SAF film is independent of the strength of antiferromagnetic coupling (AFC) between inner films. The saturation field increases with increasing the AFC strength. The spin flop field of the two- SM-layer-FC SAF film decreases, and the saturation field increases with decreasing ferromagnetic coupling strength. However, activation energy analysis demonstrates that both types of films exhibit a decrease in activation energy near the spin flop field. Considering the activation energy decrease during the toggling write sequence and a sufficient writing margin, MRAM with four ferromagnetic layers decreases writing current by 40%.

• 出版日期2007-1-15