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Will magnetic switching by light keep storage vendors spinning?

Circularly polarised lasers - the new magnetism

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Lasers are already involved in data storage, with CDs, DVDs and Blu-ray drives using laser light as well as the developing holographic drives. The HAMR development HDD technology involves the use of a laser to heat a tiny area of a hard disk drive's recording surface which then has its magnetic polarity changed via a magnetic write head.

It had been thought that it was impossible for a magnetic field to be switched between north and south poles by light. What Stanciu discovered was that it was possible to switch magnetic polarity by using circularly polarised light.

The direction of magnetism is controlled by the light's helicity, left or right. The angular momentum of the photons sets the magnetic direction. What happens is that there is localised and very fast heating of the material's magnetic systems, which renders it susceptible to the magnetic field produced by the circularly polarised pulse of light.

It is possible to produce pulses of this type of light from so-called ultra-fast or femtosecond lasers, and Stanciu demonstrated sub-picosecond magnetic switching of ferrimagnetic rare-earth-transition-metal amorphous alloys - the type of material already used, he says, in magnetic media-based data storage devices.

Two problems were identified by Stanciu in 2007 preventing the use of this method in real-life data storage. Femotosecond lasers are large and focussing a circularly polarised beam of light at the sub-micron levels required caused the polarity to suffer and the magnetic switching to be prevented.

He says that during his Seagate internship he demonstrated the effect with picosecond lasers which are less expensive and smaller than femotosecond lasers. Also, the plasmon mirrors used to focus the circularly polarised light have been improved and can now focus the light at the sub-micron level required.

Stanciu reckons that a data storage device, a laser hard drive, using this technology could have an internal channel speed of 1Tbit/s.

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