MULTILEVEL AND THREEDIMENSIONAL NANOMAGNETIC RECORDING - Bio-Inspired and Nanoscale Integrated Computing - page 190

SUL and a conventional (flat) SUL are shown in Figure 6.11a. Although for the
patterned SUL the recording field drops with the distance away from SUL, it is
still larger compared to the field in the conventional case. The graphs also indicate
that patterning of SUL would result in a more localized field. The latter effect is
discussed below in more detail.
Study of the Localization of Recording and Sensitivity Field: Patterning of
SUL is fundamentally different from patterning of the recording layer with respect
to addressing information during writing and reading. Here, it could be reminded
that SUL is an indispensable part not only of the media but also of the head [54].
The latter is not true for the recording layer. This major difference is due to the
fact that SUL is made of a ''soft'' magnetic material. This is in contrast with the
recording layer, which is made of a ''hard'' magnetic material. As a result,
patterning of SUL effectively also ''patterns'' the field generated by the head. This
field is the recording magnetic field or the sensitivity field depending on the writing
or reading processes, respectively.
To illustrate ''patterning'' of the recording field because of patterning of SUL,
two different locations of the recording head with respect to the patterned SUL
are considered, as shown in Figure 6.10b and 6.10c, respectively. In the first case,

Centered head

Patterned SUL

15000

15000

Half-period offset
head

Flat SUL

10000

10000

5000

5000

0

0

− 80 − 60 − 40 − 20 0 20 40 60 80

− 80 − 60 − 40 − 20 0 20 40 60 80

Distance across track (nm)

Distance across track (nm)

(b)

(a)

Field pattern

Field pattern

Head Head

Recording layer

(d)

Patterned SUL

(c)

Figure 6.11. (a) Field profiles inside the recording layer for the cases of patterned and
conventional SUL. (b) The field profiles along same line, 5 nm away from the surface
of SUL, along a patterned direction along or across the track. The recording field
profiles for two systems, (c) with a patterned SUL and (d) without a SUL, respectively.