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Posted: July 21, 2010
Electric-field-assisted magnetic data writing on a hard drive could improve storage densities
(Nanowerk News) The rapidly growing quantity of digital information is placing stringent demands on the storage capacity of magnetic media, such as hard drives. Increasing the number of magnetic bits stored in a given area can increase capacity but requires reducing bit size, which makes each bit more vulnerable to accidental overwriting. To compensate, researchers are exploring 'hard' magnetic materials, which have bits that are difficult to switch and therefore long-lived. However, writing to these materials with magnetic fields alone requires very high field strengths that are difficult to produce in hard drives.
This conundrum has spurred the development of techniques in which magnetic write heads are assisted by other sources of power, such as heat, microwaves or an electric field. However, the first two involve adding considerable complexity to hard drives, and the third has been completed only under unrealistic conditions. Now, under realistic conditions, Tiejun Zhou, Zhimin Yuan, Bo Liu and co-workers at the A*STAR Data Storage Institute in Singapore have demonstrated practical electric-field-assisted magnetic data writing on a hard drive ("Manipulation of magnetism by electrical field in a real recording system").
Fig. 1: An electric field applied from a hard drive recording head (yellow) induces charges (red) at the surfaces of magnetic grains (pale blue) in a thin film recording medium (gray), helping the head to write data to 'magnetically hard' recording media at high density. (Image: 2010 T. Zhou)
The researchers modified commercially available hard drive heads to allow the application of an electric field to the drive's standard recording medium, which is made of cobalt-based nanocomposite thin films (Fig. 1). Because the heads were close to the media, a low voltage of just 3 volts was sufficient to create an electric field strong enough to trap 0.15 electrons per cobalt atom in the media's grain boundaries. Previously, other researchers had observed modifications of thin film magnetic properties in the presence of such quantities of excess charge, leading Zhou and his co-workers to expect an effect in hard drives as well.
Indeed, they found that the trapped charges they induced served to reduce the energy required to switch the magnetic bits in the recording media by 26%, corresponding to a 13% reduction in the required magnetic field and an improved signal-to-noise ratio when the data was read back. The simplicity of the technique may allow it to be applied to magnetic random access memories, or to other material systems, such as iron–platinum thin films that cannot be written to using currently available recording head technologies.
The researchers plan to concentrate on developing a more complete understanding of the effect they observed. "The physics of the switching field reduction and switching mechanism needs to be studied in detail," says Liu. "This will allow the recording layer structure and materials to be optimized and the full potential of the technology to be realized."