In order to realize the density and stability advantages
of patterned media, each island must be a single magnetic
grain. During the magnetic reversal process, the islands
must switch as coherent units and not break up into
domains. After writing, each island must remain as a
single magnetic domain. Understanding the magnetic behavior
of islands with such small dimensions requires advances
in both metrology tools and in the basic science of
magnetic materials. One technique which is able to detect
and display the magnetization of magnetic island arrays
is magnetic force microscopy (MFM). Figure
4 shows an MFM image of patterned media, revealing
that each patterned island behaves as a single magnetic
domain.
Integration of Patterned Media into the Drive
Designing and fabricating the media are not the only
challenges associated with patterned media. Integrating
patterned media into a disk drive requires new technology
in synchronizing the timing of pulses in the write head
with the magnetic islands as they pass under the head,
and new methods for creating and using servo patterns
on the disk -- the guide marks that are used to keep
the magnetic head following the prepatterned track of
islands on the disk. For example, when the head pulse
is properly synchronized to the island positions, a
perfect patterned of up and down island can be written,
as shown by the MFM image in Figure
5.
Summary
Although there are many challenges to manufacturing
and using patterned media, the large potential gains
in density offered by patterned media make it one of
the most promising new technologies on the horizon for
future disk drives. Hitachi is actively engaged in research
to make the potential benefits of patterned media a
reality.
Figure 4: MFM images of small, 50 nm, single domain
islands and larger, 500nm, multidomain islands. Islands
such as the larger islands shown here are not suitable
for patterned media, as they do not have the thermal
stability and uniform magnetization required for high
density recording.
Figure 5 – AFM image of patterned islands and
MFM image of the magnetization pattern written by a
recording head. The middle panel shows the square wave
up/down pattern written, and the relative positions
of the transitions. In this example, the magnetic pattern
in perfectly synchronized to the island positions.
|
