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IBM Increases Recording Density a Thousand-Fold
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IBM Corp has developed a new medium for magnetic recording, using uniformly-spaced magnetic particles 4nm in diameter. In the future, the firm plans to record one bit of information to each particle, boosting recording density about a thousand times over present levels.
It will be extremely difficult to boost recording density with the Co-Cr materials currently used in magnetic recording, because they are composed of magnetic particles of non-uniform size, arrayed non-uniformly. Increasing the recording density will require making smaller the region needed to store one bit of information by reducing the number of magnetic particles within that region. The boundaries between the bits, however, become vague, causing noise in playback. Finer magnetic particles would resolve this problem, but then thermal fluctuation after-effects would cause the particle magnetism orientations to become unstable.
IBM's newly-developed magnetic recording material addresses these problems (see Fig). "If one bit of information can be written to a single magnetic particle, then the areal recording density would be about a thousand times higher than that of existing hard disk drives (HDD), " said an IBM spokesperson. The firm has selected FexPt1-x for the magnetic material, as it is less affected by thermal fluctuation because its magnetic anisotropy constant (Ku) is 20 to 40 times higher than that of Co-Cr.
Aligning 4nm Particles
The new magnetic recording material is made up of magnetic particles, each 4nm in diameter, arrayed neatly at 1nm intervals. Compared to existing materials where particles are randomly packed, the bit boundaries are very clear. Since particles of almost-uniform size are aligned neatly, the number of particles within a region needed to store one bit of information can be minimized. This also contributes to thermal stability.
When Co-Cr material is used, a single region requires several hundred to a thousand particles, but according to Dieter Weller, research staff member, Magnetic Recording Materials, Research Division of IBM, the new magnetic media would only need "under a hundred." As a result, assuming the area and the film thickness of the region needed to store one bit are equal to conventional media, then the volume of a single particle can be increased. As a result, even with the same magnetic anisotropy constant, a material with an orderly structure (like the new material) resists thermal fluctuation after-effects better.
Two polymers, containing Fe and Pt each, are reacted to create colloidal particles encapsulating the Fe x Pt 1-x magnetic particles. Diameter is from 3 to 10nm, depending on reaction parameters. When the colloid is coated on the substrate, polymer composition causes the Fe x Pt 1-x particles to be aligned uniformly. The resultant thin-film is thermal-processed to leave only the carbon atoms of the polymer molecule, which serve as magnetic barriers between the magnetic particles.
One Particle, One Bit
If IBM is able to record one bit of information in each particle using the new material, then it should be possible to achieve an areal recording density of 20 Tbits/inch 2 . There are a number of technical hurdles to be cleared first, however.
The key problem is the positioning of the record and play heads. The conventional record/play system uses a group of magnetic particles to store 1 bit of information, and the recording region is determined by the head position. When 1 bit is handled by a single particle, however, the heads must be positioned accurately on individual particles. This means that magnetic particles must be aligned with a precision on the level of photolithography, and record/play heads must be developed capable of processing information from a single particle.
It will also probably be necessary to increase the physical durability of the media surface. The carbon atoms separating the particles are relatively weaker than the B and Cr atoms performing the same task on existing media.
Since it is impossible to immediately begin recording one bit per particle, for the time being systems will continue to use multiple particles to store 1 bit of information. "We are aiming at 100 Gbits/inch 2 to start off with," said Weller. The new material is superior to Co-Cr not only because of its smaller particle size, but also because size variation has been reduced to only +/- 2.5%.
by Hiroki Eda
(July 2000 Issue, Nikkei Electronics Asia)
It will be extremely difficult to boost recording density with the Co-Cr materials currently used in magnetic recording, because they are composed of magnetic particles of non-uniform size, arrayed non-uniformly. Increasing the recording density will require making smaller the region needed to store one bit of information by reducing the number of magnetic particles within that region. The boundaries between the bits, however, become vague, causing noise in playback. Finer magnetic particles would resolve this problem, but then thermal fluctuation after-effects would cause the particle magnetism orientations to become unstable.
IBM's newly-developed magnetic recording material addresses these problems (see Fig). "If one bit of information can be written to a single magnetic particle, then the areal recording density would be about a thousand times higher than that of existing hard disk drives (HDD), " said an IBM spokesperson. The firm has selected FexPt1-x for the magnetic material, as it is less affected by thermal fluctuation because its magnetic anisotropy constant (Ku) is 20 to 40 times higher than that of Co-Cr.
Aligning 4nm Particles
The new magnetic recording material is made up of magnetic particles, each 4nm in diameter, arrayed neatly at 1nm intervals. Compared to existing materials where particles are randomly packed, the bit boundaries are very clear. Since particles of almost-uniform size are aligned neatly, the number of particles within a region needed to store one bit of information can be minimized. This also contributes to thermal stability.
When Co-Cr material is used, a single region requires several hundred to a thousand particles, but according to Dieter Weller, research staff member, Magnetic Recording Materials, Research Division of IBM, the new magnetic media would only need "under a hundred." As a result, assuming the area and the film thickness of the region needed to store one bit are equal to conventional media, then the volume of a single particle can be increased. As a result, even with the same magnetic anisotropy constant, a material with an orderly structure (like the new material) resists thermal fluctuation after-effects better.
Two polymers, containing Fe and Pt each, are reacted to create colloidal particles encapsulating the Fe x Pt 1-x magnetic particles. Diameter is from 3 to 10nm, depending on reaction parameters. When the colloid is coated on the substrate, polymer composition causes the Fe x Pt 1-x particles to be aligned uniformly. The resultant thin-film is thermal-processed to leave only the carbon atoms of the polymer molecule, which serve as magnetic barriers between the magnetic particles.
One Particle, One Bit
If IBM is able to record one bit of information in each particle using the new material, then it should be possible to achieve an areal recording density of 20 Tbits/inch 2 . There are a number of technical hurdles to be cleared first, however.
The key problem is the positioning of the record and play heads. The conventional record/play system uses a group of magnetic particles to store 1 bit of information, and the recording region is determined by the head position. When 1 bit is handled by a single particle, however, the heads must be positioned accurately on individual particles. This means that magnetic particles must be aligned with a precision on the level of photolithography, and record/play heads must be developed capable of processing information from a single particle.
It will also probably be necessary to increase the physical durability of the media surface. The carbon atoms separating the particles are relatively weaker than the B and Cr atoms performing the same task on existing media.
Since it is impossible to immediately begin recording one bit per particle, for the time being systems will continue to use multiple particles to store 1 bit of information. "We are aiming at 100 Gbits/inch 2 to start off with," said Weller. The new material is superior to Co-Cr not only because of its smaller particle size, but also because size variation has been reduced to only +/- 2.5%.
by Hiroki Eda
(July 2000 Issue, Nikkei Electronics Asia)
