Initially, magnetic tapes and disks used iron oxide in a binder on either a rigid or flexible substrate. Later, techniques were developed to (somewhat) control the shape and orientation of magnetizable particles. Eventually media split into "hard" and "soft" media. Hard media require strong fields for recording, but offer high data densities and low drop out rates. "Soft" materials use smaller recording fields, and offer better linearity for intermediate values. Hard materials are used primarily for digital recording, Soft materials are used primarily for analog recording.
Early devices used a variety of magnetic materials including magnetite, Iron carbonyl and Barium ferrite. However, the primary material used has been ferric oxide. Occasionally Iron or Chromium Dioxide are used. Cobalt is sometimes mixed with ferric oxide to improve the coercivity (magnetization density). Small amounts of other metals may be present as a result of processing steps to control crystal shape and orientation. The basic chemistry/physics of recording materials have not changed greatly over the years although the technologies for applying them and controlling the crystal size and orientation have.
Plastic binder and substrate materials are used for tapes or flexible disks. For rigid disks, aluminum or glass substrates are generally used. Media may be rolled on or deposited as a film by plating, evaporation or sputtering.
Return To Index Copyright 1994-2002 by Donald Kenney.