Correlation of detailed microstructural information obtained from a temperature series (25–275°C) of otherwise identical CoCrTa/Cr recording media with detailed recording performance measurements demonstrates two mechanisms for magnetic isolation.
Media were prepared by sputter deposition of 75 nm Cr underlayers and 60 nm Co84Cr12Ta4 layers onto circumferentially textured NiP plated aluminum substrates using an Intevac MDP-250 machine.
High-resolution transmission electron microscopy (HRTEM) and high-resolution scanning electron microscopy (HRSEM) show columnar isolation by voiding, via the mechanism of shadowing during low temperature growth. Shadowing decreases with increasing temperature until voiding disappears at 150°C. At high temperature (275°C), large intergranular separation is observed, which has been attributed to elemental segregation. This separation decreases as temperature decreases, until it disappears at 150°C.
Detailed magnetic recording measurements show that the maximum normalized media noise power is observed at 150°C. It decreases as more isolated structures are formed by increasing or decreasing temperature. Uniform magnetization noise, a measurement related to crosstrack correlation length within a magnetization transition also shows this trend.
It is suggested that HRTEM shows two different microstructural features that control magnetic correlation lengths and resulting media noise.