Recording performance of the perpendicular recording media with an electroless-plated Ni-P soft magnetic underlayer

An electroless-plated ferromagnetic Ni-P layer, which is suitable for mass production, was employed as a soft magnetic underlayer (SUL) for a double-layered perpendicular recording media. A Ni-P SUL with a thickness range from 1.5 to 3.0 μm was plated on the Al substrate, then the surface of the Ni-P SUL was polished about 1 μm to obtain a smooth surface with a roughness Ra of less than 0.3 nm. The saturation flux density B_s and the in-plane coercivity H_c for the Ni-P SUL were about 0.5 T and 15∼20 Oe, respectively. Media with a Ni-P SUL at a thickness of more than 0.5 μm showed almost the same magnetic properties and recording performances as a medium with a 200-nm thick sputtered CoZrNb SUL. Furthermore, the spike noise commonly observed from an SUL was not found for the media with the Ni-P SUL in this study, indicating great potential for the electroless-plated ferromagnetic Ni-P layer as the SUL of the perpendicular recording media.