Conventional approaches to magnetic data storage are expected to offer a maximum storage density of about one terabit per square inch. Any attempts to go above this limit by using smaller bit sizes will be thwarted by the problem of superparamagnetism — random changes in the magnetization direction of small particles. It is possible to avoid the superparamagnetic effect, but only at the expense of increasing the switching field to values above those that can be produced by the magnetic write head.
Researchers have been exploring various ways to overcome these challenges, and now Barry Stipe and co-workers at Hitachi research centres in the US and Japan have shown that two new approaches — thermally assisted magnetic recording and the use of bit-patterned recording media rather than continuous media — can be combined to solve many of the problems associated with superparamagnetism. Thermally assisted magnetic recording involves heating the storage medium to reduce the switching field.
Of course, heating very small regions is a technical challenge, and the Hitachi team include a thin-film waveguide and a plasmonic nanoantenna in their recording head for this purpose. The waveguide directs near-infrared light from a laser diode to the nanoantenna, which focuses the light into a region measuring about 30 nm across. Stipe and co-workers report storage densities of one terabit per square inch — which is the limit of conventional approaches — and claim that much higher densities are possible.
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To the limit and beyond. Nature Nanotech (2010). https://doi.org/10.1038/nnano.2010.123
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DOI: https://doi.org/10.1038/nnano.2010.123
