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Heat-Assisted Magnetic Recording

Storage density of magnetic hard drives has continued to grow through the last decade but increases in density have begun to wane as a result of the super paramagnetic limit causing an instability in the stored data. The fundamental technical challenge is that it is not possible to generate large enough magnetic fields to overcome the extremely high magnetic anisotropy necessary for media thermal stability. A promising approach is to temporarily reduce the magnetic anisotropy of a medium via increasing the medium’s temperature, write in the bits, and rapidly cool down the medium to freeze in the magnetization state of the bits. The major challenge is that only the area to be recorded into should be heated to avoid thermal instabilities in adjacent bits and tracks. At “modest” densities of 1Tbit/in2, the heat needs to be delivered to a 26nm by 26nm square spot. At 50 Tbits/in2 the size to be heated is below 4nm by 4nm.

A similar project driven by the International Storage Industry Consortium attempts to deliver heat via near-field optics. There are significant challenges to deliver a sufficient light intensity to a spot that is several orders of magnitude smaller than the wavelength of the laser being used.

Our alternative approach to heat assisted magnetic recording (HAMR) is to use electrons and joule heating generated by electron current to raise the temperature of the bits. For the approach to succeed, the availability of low voltage cold emitter materials is critical. The recording head in today's recording is in near contact with the medium (flight-height is about 5nm). The emitted electrons will have to travel a very short distance to reach the medium to be heated, thus, it will likely not be necessary to seal the storage device in a vacuum package. If necessary, however, sealing a storage device in an inert gas atmosphere is a viable option because it is being seriously considered by the industry for several unrelated reasons.

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