A Co/Pd multilayered film is one of the promising perpendicular magnetic recording (PMR) media with high magnetic squareness, due to interfacial magnetic anisotropy energy. However, the lack of a magnetic decoupling factor in the Co/Pd film, unlike a compositionally decoupled CoCr based alloy film, possesses large magnetic exchange energy which results in large magnetic domain sizes and high noise source. In this research, we investigate a domain isolation parameter (α) to control the magnetic exchange energy and domain sizes in terms of the deposition pressures of a Co/Pd recording multilayer and a Pd buffer layer in a PMR disk. The high pressure in the Pd buffer layer is effective to isolate and reduce the Co/Pd domain sizes with a low α value. The observations with a magnetic force microscope (MFM) and a cross sectional transmission electron microscope (TEM) prove that the physically decoupling effect originated from the surface roughness of the Pd buffer layer, plays a major role in creating a fine domain pattern in the Co/Pd multilayer. The dynamic read/write performances of the Co/Pd multilayered disk by a merged giant magneto resistive (GMR) head show that the low α value disk with magnetically decoupled grains has a low medium noise level, compared with the high α value disk.