140 CHAPTER 13. HIGH-DENSITY RECORDING MATERIALSThe second method is based on so-called perpendicular magnetic recording, in which
materials are used that have an enhanced perpendicular magnetization component. These
perpendicular recording materials have a high anisotropy. The preferred magnetization
direction is perpendicular to the film plane, which inhibits the formation of the circular
polarization mode. Thin films of Co–Cr alloys possess such favorable properties. They
make it possible to obtain sharp transitions between domains of opposite magnetization,
which is a prerequisite for high-density recording.
The two types of magnetic recording, longitudinal and perpendicular, are compared in
Fig. 13.3.2. Step-like changes in the initial distribution of the magnetized areas in the
medium would occur if the recording process were an ideal one. This is indicated in