Grain-based magnetic recording can achieve 10Tb per square inch

One method under current investigation is storing each data bit in a single magnetic grain of the thin film of the recording medium, rather than in several grains as in conventional hard drives. Storage in single grains only would increase stability and reduce the magnetic fields required to write bits. By modeling write processes in hard disks, Melissa Chua and her co-workers at the A*Star Data Storage Institute in Singapore, have demonstrated how this is possible in practice.

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Thin magnetic films for data storage coat the top layer of plastic films in hard-disk drives and consist of many neighboring nanometer-sized grains. As storage density of magnetic films has increased over the years, the surface area used for storage per bit is now comparable to the size of these grains.