Thin-film media for increasing the recording density on magnetic hard disks have been obtained by sputtering or plating, and since these media require a comparatively flat substrate, electroless Ni-P plating is employed to harden the surface and facilitate polishing To be used successfully, the process must be satisfactory in terms of such properties as finished final surface roughness, magnetization, and adhesion The object of the present work is to examine various pretreatments for 5086 Al-alloy, the most common material used for hard disk substrates. Results indicate that the optimum process was one consisting of alkaline non-etch cleaning, hot acid etching and double zincate treatment. This produced a homogeneous and thin zinc film. Though deeper etching improved adhesion, it also increased roughness after plating
An advanced electroless cobalt plating bath has been developed for increasing the recording density of 3.5″ hard disks, and its properties and magnetic film were analyzed Based on an investigation of many chelate agents of a plating bath, high coercivity and stability was obtained, and it was possible to obtain high S* and output by adding specific salts to the bath, while the addition of zinc resulted in low noise media having fine cristalite The use of a plating bath adjusted to an Hc of 1100Oe made it possible to achieve storage capacities of 40MB on 35″ disks
The effect of circumferential texturing on the magnetic and microstructural properties of electroless-plated CoP thin films for high-density longitudinal magnetic recording media was investigated. The texturing was found to induce magnetic anisotropy of the CoP thin films along the circumferential direction, causing an increase in coercivity (Hc, coercive squareness (S*) and SQR (Mr/Ms) values in that direction. SEM observation revealed that grains of the CoP film deposited on the textured substrate formed a coagulum along the grooves. It is therefore suggested that the magnetic anisotropy of the film is due to the shape anisotropy caused by such film morphology.
Codeposition of zinc remarkably reduces the media noise in electroless plated disks. This study was designed to investigate the effects of zinc on the noise and magnetic properties of textured plated disks Codeposition of zinc reduces the grain size of the film and improves S/N ratio of the disk In terms of the magnetic properties, the addition of zink was found to result in a decrease in squarness and anisotropy in coercivity between the circumferential and radial directions TEM-EDX analysis showed segregation of zinc and phosphorous at the grain boundaries of the film, and this segregation decreased the magnetic interaction at grain bounndaries and consequently reduced the media noise Both zink and phosphorous in the film were found to exist in a metallic as well as an ionic state, ratio between these states being dependent on the pH of the plated bath
The absorption spectra of electroless cobalt alloy plating baths and the magnetic properties of the plated films were investigated in order to find complexing agents suitable for plating baths for high-density recording media. In screening tests in which various complexing agents were introduced into caustic alkaline cobaltous solution, cobalt-citrate-aminoacetate complex was selected as the optimum mixed complex. Magnetic properties of the plated films varied greatly, depending on which complex-cobalt-citrate or cobalt-aminoacetate-become dominant in the mixed complex bath. Based on studies of the effects of bath factors on complex behavior and magnetic properties, a fundamental CoP bath composition was established such that a steady coercive force of 700Oe would be obtained. To increase the coercive force, the effect of adding zinc to the CoP bath was studied, and a maximum of 1700Oe was obtained. Read/write evaluation tests revealed that the output voltage and SNR of the CoZnP plated disk (Hc≅1200Oe) represented increases of about 30% and 5dB respectively over those of the CoP plated disk (Hc≅700Oe).