One promising route to achieving densities beyond
the apparent limits of the superparamagnetic effect
is patterned media. With patterned media (see Figure
2), each bit is stored in a single deliberately
formed magnetic switching volume. This may be one grain,
or several exchange coupled grains, rather than a collection
of random decoupled grains. Single switching volume
magnetic islands are formed along circular tracks with
regular spacing. Magnetic transitions no longer meander
between random grains, but form perfectly distinct boundaries
between precisely located islands.
Since we no longer need on the order of 100 grains
per bit, but just one single grain-sized switching volume,
density can be increased by roughly two orders magnitude
compared to conventional recording media. Since each
island is a single magnetic domain, patterned media
is thermally stable, even at densities far higher than
can be achieved with conventional media.
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