text: Magnetic recording relies on the use of hard ferrimagnetic or ferromagnetic materials. These require strong external magnetic fields to be magnetized, and retain substantial residual magnetization after the magnetizing field is removed. Two fundamental magnetic properties, relevant for audio recording, are:
  * Saturation remanence limits maximum output level and, indirectly, dynamic range of audio recordings. Remanence of audio tapes, referred to quarter-inch tape width, varies from around  for basic ferric tapes to  for Type IV tapes; advertised remanence of the 1986 JVC Type IV cassette reached .
  * Coercivity is a measure of the external magnetic flux required to magnetize the tape, and an indicator of the necessary bias level. The coercivity of audio tapes varies from  to . High-coercivity particles are more difficult to erase, bias and record, but also less prone to high-frequency losses during recording, and to external interference and self-demagnetization during storage.
  A useful figure of merit of tape technology is the squareness ratio of the hysteresis curve. It is an indicator of tape uniformity and its linearity in analogue recording. An increase in the squareness ratio defers the onset of compression and distortion, and allows fuller utilization of the tape's dynamic range within the limits of remanence. The squareness ratio of basic ferric tapes rarely exceeds 0.75, and the squareness ratio of the best tapes exceeds 0.9.