Soft-magnetic underlayer for MP data tape

The high output at long wavelengths of MP tape causes problems with the nonlinear response of magneto-resistive reading elements. Thinner magnetic coatings would solve the problem but it is easier to add a soft magnetic underlayer to flatten the frequency response. Superparamagnetic maghemite is a suitable material for a particulate soft magnetic underlayer. It has the appropriate particle size and can be prepared in an easily dispersible form. Both the susceptibility and the saturation magnetization achieved in the coating are limited compared with continuous soft magnetic materials. However, the nonlinear saturating effect partly compensates the disadvantage of a low initial susceptibility, while at the same time limiting potential harm to the recording process.