SECTION 14.5. HEAD MATERIALS AND THEIR APPLICATIONS 159
Accordingly, and are seen to pass through a maximum in this grain-size regime.
When the grain size has eventually become so large that it exceeds the domain-wall width,
domains can be formed within the grains. As a consequence, and tend to decrease
again according to the well known 1/D law (see Eq. 14.1.3).14.5. HEAD MATERIALS AND THEIR APPLICATIONS14.5.1. High-Density Magnetic-Induction HeadsA conventional inductive recording head consists of a slit toroid of a high-permeability
material wound by several conductor turns. A schematic representation is shown in
Fig. 14.5.1.1. The output voltage V of the head is determined by Faraday’s law (Eq. 8.7)
and hence by the flux changes due to the medium when passing along the slit. However,
in the setup shown in the figure, also the field H(x, y, z) produced by a current i passing
through the head windings is of influence. It can be shown that the following expression
holds for the output voltage V (Mee and Daniel, 1990):
where M(x, y, z) is the magnetization of the medium, and v is the medium velocity in the
x direction.
It follows from Eq. (14.5.1.1) that the output voltage depends on the velocity v of the
medium relative to the head. This implies that the larger the speed of the medium, higher
is the sensitivity. In some applications where a high sensitivity and a high storage density
are required (video applications and several audio and data-processing applications) one