Physics of Magnetism

SECTION 14.5. HEAD MATERIALS AND THEIR APPLICATIONS 161

eddy currents. To ensure good reliability and a long operating life, the materials must exhibit
a good thermal stability and a high resistance to wear and corrosion. Table 14.5.1.1 lists a
number of materials used for inductive-head applications.

14.5.2. Magnetoresistive Heads

In the early 1970s, a novel type of reading heads was introduced, based on several
types of transition-metal alloys such as Ni–Fe, Ni–Co, and Co-Fe. The working principle
of these heads is the magnetoresistive effect, which entails a decrease of the electrical
resistivity when the direction of the applied current is rotated away from the magnetization
direction.
The magnetoresistive heads have characteristics that are fundamentally different from
those of the inductive heads described in the preceding section. In its simplest form, the head
consists of a narrow sensor strip of height h and width w mounted in a plane perpendicular
to the moving recording medium. It is connected to leads at each end carrying a sense
current I as shown in Fig. 14.5.2.1.

and the current-density

vector

Due to the magnetoresistive effect, the electrical resistivity of each portion of this strip
depends on the angle between the direction of magnetization

In most of the conventional transition-metal alloys, the values of are 2–6%. Values
of about an order of magnitude higher can be reached in special alloys consisting of small
ferromagnetic single-domain particles in a non-magnetic metallic medium (granular films).
High values of are also reached in multilayer films. Multilayer thin films and granular