Si-doping of Co/Pd multilayers for improved signal to noise in perpendicular magnetic recording media

Co/Pd-based multilayers have been Si doped in order to enhance their potential for extremely high-density perpendicular magnetic recording (PMR) media. Co/Pd multilayers have high interface-induced perpendicular anisotropy, high coercivity, and high remnant squareness, all of which make them excellent candidates for PMR. Dopants can be utilized to reduce grain size as well as to reduce magnetic coupling between grains via compositional segregation to the grain boundaries. Here, Si was chosen for a dopant because the phase diagrams indicated that Si may migrate to form silicides at the grain boundaries. An additional benefit of Si as a dopant is that it can be detected chemically, unlike the more common dopant B, which is a much lighter element. A significant difference between the current doping and all other doping in PMR media is that Si was added into the Pd layers rather than the Co layers, which keeps the magnetic layer pure and improves the magnetic properties. This media was also made at room temperature, which yields smaller grains and reduces interfacial diffusion. The static magnetic properties of the Si-doped multilayers were very promising as measured by vibrating sample magnetometry: Hc = 5400 Oe, Ms = 160 emu/cm³, and α = 4πdM/dH ≈ 1. The fact that the latter term was unity suggests that the grains are magnetically decoupled which promises low transition noise. The samples were measured by atomic force and magnetic force microscopy (AFM/MFM) and by X-ray scattering. They were found to have 12-nm grains. In addition, Si-doped multilayer media that were spin-stand tested showed an increase in signal-to-noise ratio of 5 dB compared to high-performing B-doped media.