In developing magnetic recording disks based on gamma ferrite (Fe2O3) thin film media and having very low level noise and high corrosion resistance, it is necessary to oxidize magnetite (Fe3O4) to gamma ferrite by heat treatment at temperature of 300°C or higher. This requires a new underlayer that is non-magnetically stable under such severe conditions. Based on a report by Osamu Takano on Ni-Cu-P, experiments were conducted to vary the [Ni2+]/[Cu2+] ratio in the Ni-Cu-P bath to determine how heat treatment affect non-magnetic characteristics. It was found that by varying the [Ni2+]/[Cu2+] ratio deposits with a wide range of Ni or Cu contents could be plated. Films containing less than 60% Ni showed non-magnetically stable characteristics even after severe heat treatment. It was concluded that electroless Ni-Cu-P opened the way to development of high quality magnetic recording disks.
A soft magnetic undercoating layer for perpendicular recording media was prepared by electroless plating method, and the most optimum plating conditions were investigated. The iron content of nickel-iron-phosphorus films varied from 0 to 18% with the ferrous sulfate concentration in the plating solution. The addition of iron to nickel-phosphorus plating film decreased their coercive force and increased squareness. Film deposited from the most optimum plating solution exhibited coercive force of 1.0 Oe and squareness of 0.95 and showed strong (111) plane orientation, which improved the anisotropy of perpendicularly magnetized film.
Electroless plated Co-Ni-Re-P alloy films for perpendicular magnetic recording media were investigated in order to clarify the origin of perpendicular coercivity, Hc (⊥), at the initial deposition stage. The perpendicular coercivity, Hc (⊥), contained a somewhat various Hc (⊥) component. From the coercivity angular variation measurement, the magnetization reversal of all films was found to obey the rotational mechanism. The columnar structure could not be observed clearly by SEM observation. It was confirmed that the Hc (⊥) value difference at the initial deposition stage was caused by the different degree of c-axis orientation. The capability of electroless plating for perpendicular magnetic recording media preparation is widen by the control of the degree of c-axis orientation at the initial deposition stage, without change in the magnetic reversal mechanism and cross section morphology.
The effect of additive elements was examined with view to improving the reliability of magnetooptical recording media using terbium-iron based material. First static measurement indicated that Pt, Al, Ti and Cr were effective in suppressing the necleation and growth of pin-holes that cause degradation of the error rate. Pt was also found to suppress the degradation of Kerr rotation angle and reflectivity. Life time tests on disk containing Pt showed that Pt had the effect of extending lifetimes by at least two times at room temperature, whether the disk had a protective layer or not.
The properties of a Ni-Cu-P (appr. Cu 40 wt%) film, for use as a haed disk undercoat were investigated. Electroless Ni-P films are currently handling this task with one limitation, Ni-P deposited films can not remain non-magnetic at post 300°C heat treatment temperatures. Ni-Cu-P electroless deposited films have been proven to maintain total non-magnetism even after 400°C heat treatment for three (3) hours. And yet provide the hardness which is so valuable in traditional Ni-P films. We further detailed how Ni-Cu-P films could provide an inexpensive and highly reliable undercoating.
Very dense films can be deposited on substrates at a high rate without undesirable influences of the plasma using the Facing Targets Sputtering (FTS) system, and aluminum films 0.7 to 1.5μm thick have been deposited in an argon gas pressure PAr of 9.7×10-2 to 2.0Pa. Grains of irregular shape grew larger as PAr increased. When a bias voltage to the substrate Vb of-40V was applied, however, the number of grains per unit area decreased and grain became smaller, so that the film surfaces became smooth. At Vb of about -40V the aluminum films became hardest twice as hard as films prepared without bias voltage. Thus the FTS system can control film properties with a good reproducibility.