Heat-assisted magnetic recording (HAMR) is a magnetic storage technology for hard drives in which a small laser is used to heat the part of the disk that is being written to. The heat reduces the coercivity of the material, hence allowing the head to write on materials with higher coercivity, which in turn allow for smaller grain size which is limited by the superparamagnetic effect hence increasing the maximum possible areal density. The net effect of HAMR is to allow writing on a much smaller scale than before, greatly increasing the amount of data that can be held on a standard disk platter.
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The technology was initially seen as extremely difficult to achieve, with doubts expressed about its feasibility. As of 2016, no hard disks using HAMR are currently on the market, but HAMR is in an advanced state of development with demonstration drives produced by companies such as Seagate. While TDK originally predicted that HAMR hard disks could be commercially released in 2015, the best estimate as of December 2015 is that they will arrive in 2018.
Overview
There have been a series of technologies developed to allow hard drives to increase in capacity with little effect on cost; one of the latest is perpendicular recording. To go beyond the limits of perpendicular recording, new technologies are being developed, including helium-filled drives, shingled magnetic recording (SMR), as well as heat-assisted magnetic recording ("HAMR").
The limitation of perpendicular recording is often characterised by the competing requirements of readability, writeability and stability commonly known as the Magnetic Recording Trilemma. HAMR is one technique proposed to break the trilemma and produce a workable solution. The problem is that to store data reliably for very small bit sizes the magnetic medium must be made of a material with a very high coercivity. At increasing areal densities, the size occupied by one bit is so small, and the coercivity required becomes so high, that the strongest magnetic field able to be created for writing data with current technology is not strong enough to flip the magnetic domain. In effect, a point exists at which it becomes impractical or impossible to make a working disk drive because magnetic writing activity is no longer viable.
Coercivity happens to be temperature dependent. If the temperature rises then the coercivity would be lower. HAMR uses this physical behavior to solve the problem. In HAMR, a small laser is used to temporarily spot-heat the tiny area being written to at any given time. When the temperature of the area being written is raised in this way above the Curie temperature, the magnetic medium effectively loses much of its coercivity, so a realistically achievable magnetic write field can write data to the medium. As only a tiny part of the disk is heated at a time, the heated part cools very quickly, and comparatively little power is needed.
HAMR could eventually increase the limit of magnetic recording by more than a factor of 100. This could result in storage capacities as great as 50 terabits per square inch. Running costs are not expected to differ significantly from non-HAMR drives, since the laser only uses a few tens of milliwatts (around 1% of the common 5 to 12 watts in active use of large 3.5 inch HDDs). It competes with technologies such as SMR.
Industry observer IDC stated in 2013 that "The technology is very, very difficult, and there has been a lot of skepticism if it will ever make it into commercial products", with opinions generally that HAMR is unlikely to be commercially available before 2017. Seagate commented that the challenges include "attaching and aligning a semiconductor diode laser to an HDD write head and implementing near-field optics to deliver the heat", along with the scale of use which is far greater than previous near-field optic uses.