Switching characteristics of submicrometer magnetic tunnel junction devices with perpendicular anisotropy

As the pattern size of magnetic tunnel junctions (MTJs) becomes smaller, the vortex of magnetization and fluctuations of switching fields caused by the shape MTJ cells will cause serious writing problems. However, a MTJ structure with perpendicular anisotropy (pMTJ) has shown low saturation magnetization and shape independence during the writing process. In this study, we considered CoPd multilayers that allow better tailor-design of magnetization and anisotropy. A series of calculations based on the Landau-Lifschitz-Gilbert equation were carried out on pMTJs to investigate the effect of size variations and material properties on their transfer behaviors. In a same submicrometer cell size, pMTJ shows better properties for high-density magnetoresistive random access memory (MRAM) against synthetic antiferromagnet MTJs. As the number of bilayer CoPd, n, becomes larger, the coercivity and squareness were enhanced because of shape anisotropy and large effective Ku. Even with a small field, 10 Oe, along the hard axis, the drastic decrease, nearly about 80% of switching field, occurs. As a micromagnetic result, a pMTJ with a cell size of 200 nm and n=3 shows an abrupt increase in coercivity and better squareness.