MULTILEVEL AND THREEDIMENSIONAL NANOMAGNETIC RECORDING - Bio-Inspired and Nanoscale Integrated Computing - page 184

Inductive “SPH”
head

Magnetizing
coils
Reader
(GMR sensor)

head

H = H c

Magnetic
bits

Write field

Magnetization up and down

(a)

SUL

(b)

Nanoprobe

Writer (single pole)

FIB − etched regions

GMR reader

(c) (d)

Figure 6.6. (a) Schematic illustrating recording across the thickness via continuous
variation of the recording field. The boundary curve is the field profile when H=H c ,
where H c is the coercivity. (b) A diagram of a perpendicular recording system. FIB
images of FIB-fabricated (a) single pole writer with a 80-nm trackwidth and (b) a MFM
nanoprobe for reading a component of the stray magnetic field.

media are shown in Figure 6.7b. A digitized sectional profile of the signal along
the highlighted line going through a track of bits is shown above the AFM and
MFM images. Clearly, over three different signal levels could be detected, as
shown in Figure 6.7b (top).
This experiment illustrates that the 3D media could be partially polarized
across the thickness, resulting in a multilevel signal configuration. On the
contrary, it is known that in conventional recording the magnetization remains
in one of the two saturated states and no partial polarization is feasible. To further
perfect the concept of generating a multilevel signal, various types of media have
to be developed and explored. However, media development is not the main
subject of this chapter. Instead, the focus is placed on the system integration.