Physics of Magnetic Recording and Recording Media Lecture Note

Magnetic recording media in the form of disks are either magnetic particle based or continuous magnetic thin film based. In the case of particles, an organic binder is used to retain these magnetic particles. Modern magnetic disks are mostly thin film based and have complex multilayer structures. Figure 1.55 shows an example of magnetic thin film based disk media. It has an alumina substrate that is coated with NiP, often called an undercoat layer. This undercoat layer provides stiffness, smoothness and proper texture to the media. This is coated with a chromium layer prior to the deposition of the magnetic recording layer, which is usually a cobalt alloy. Both chromium and cobalt alloy films are typically deposited using sputtering.

The magnetic layer is then coated with a carbon overcoat layer and a lubricant layer. These two layers are required to protect the magnetic layer from tribological wear at the head–disk interface because of the high speed (>5000 rpm) rotation of the disk underneath the flying head. The distance between the head and the top disk surface (fly height) is typically of the order of a few tens of nanometers (nm). This height is a fraction of the distance between the head pole tip and the magnetic layer (magnetic spacing).

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