160 CHAPTER 14. SOFT-MAGNETIC MATERIALS
therefore does not employ stationary heads but rotating heads. Heads in modern magnetic
storage systems are designed in a way that they can develop a hydrodynamic and self-acting
air bearing under steady operating condition, which minimizes the head–medium contact.
There is only physical contact between the medium and the head during the starts and stops.
In modern data-storage tape and disk drives, the head-to-medium separation is of the
order of 0.1–0.3 mm, the head and medium surfaces have roughnesses of the order of
2–10 nm. The need for higher recording densities requires that the surfaces be as smooth as
possible and the flying heights as low as possible. A schematic representation of a recording
process is shown in Fig. 14.5.1.2.
In general, one may distinguish between two types of heads, magnetic inductive heads
and magnetoresistive heads. There are two different physical principles involved in these
heads. Consequently also the material requirements for the two types are different. In the
next two sections, both types of materials will be briefly discussed.
Soft-magnetic materials are widely employed for the fabrication of magnetic recording
heads. These materials must have a high saturation magnetization in order to produce a large
gap field. A high permeability is required in order to ensure high efficiency and a small
magnetostriction in order to ensure low medium-contact noise. The coercivity has to be low
in order to ensure a low thermal noise, and a high electrical resistivity in order to reduce