Cu-Containing [Pt/Co] multilayers with low saturation magnetization suitable for the pinned structure

We prepared [Pt/(Co, Cu)] multilayers with a very thin (i.e., 0.2 nm thick) Pt layer and a thicker (i.e., 0.4, 0.5, or 0.6 nm thick) (Co, Cu) layer and investigated the effects of the Cu content in the (Co, Cu) layer and the postannealing temperature on the magnetic properties of the multilayers. The samples in the as-deposited state and those annealed up to 500 °C for 1 h all exhibited perpendicular magnetic anisotropy (PMA). The PMA strength and saturation magnetization both decreased with increasing content of Cu in the samples. The saturation magnetization of the Cu containing multilayers annealed at 500 °C substantially decreased, probably owing to the change in the microstructure from a layered structure in the as-deposited samples to a bulk phase in the annealed ones, as supported by high resolution transmission electron microscopy images. The effective PMA energy density of the samples annealed at high temperatures, on the other hand, remained nearly unchanged and even increased slightly indicating a high postannealing stability of Cu containing multilayers. The Cu-containing multilayers may find potential application to high density magnetic random access memory as the pinned structure of magnetic tunnel junctions because the multilayers showed low saturation magnetizations in the range 164-753 emu/cm³ and high postannealing stability.