Recording characteristics of coated disks having high coercivity powder

The recording characteristics of coated disks having high coercivity powder, in particular metal powder, are given. We manufactured various disks containing γ-Fe2O3(coercivity: 350 Oe), iron-cobalt metal powder (400 - 800 Oe) and iron metal powder (650 Oe), respectively. The recording characteristics of these disks were measured by using a Mn-Zn ferrite head whose saturation magnetization was 5,000 gauss. It was found that disks with higher coercivity showed a capacity for increased bit density, but at the same time, poor overwrite characteristics. The optimum coercivity proved to be about 650 Oe. The typical values for metal powder coated disks (650 Oe) were: critical bit density: 19,000 BPI reproduced output: 1 mV at 19,000 BPI overwrite: -30 dB.