SECTION 13.3. MATERIALS FOR HIGH-DENSITY MAGNETIC RECORDING 145
Thin magnetic films have replaced most of the particulate media in rigid-disk drives and
are preferred media in videotape applications. Lodder (1998) has presented a comprehensive
review of such media. An illustration of the vapor-deposition process is given in Fig. 13.3.5.
The electron gun consists of a hot-metal filament from which electrons are emitted via a high
voltage. The beam of electrons is directed into the crucible containing the master alloy via
magnetic fields that can deflect this beam. The evaporation rate of the alloy can be adjusted
instantaneously by adjusting the power generating the electron beam. The orientation of the
crystallites in the film depends on the position of the crucible. In the arrangement shown in
the figure, a curved columnar structure of the magnetic layer is obtained. Tapes prepared
by this oblique-evaporation technique are used for longitudinal recording. Thin magnetic
films used for perpendicular recording are prepared by a symmetrical arrangement of the
source relative to the tape. In this case, a columnar structure is obtained with the column
axes perpendicular to the film plane. Co–Cr alloys are a preferred medium for perpendicular
recording.
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