Heat-assisted magnetic recording
Heat-assisted magnetic recording (HAMR) is a technology that magnetically records data on high-stability media using laser thermal assistance to first heat the material. HAMR takes advantage of high-stability magnetic compounds such as iron platinum alloy. These materials can store single bits in a much smaller area without being limited by the same superparamagnetic effect that limits the current technology used in hard disk storage. This is achieved by heating the materials before applying the changes in magnetic orientation. No hard disks using HAMR are currently on the market, but HAMR is expected to eventually become the technology used for hard disk drives with higher capacities than is possible today.
- In 1954, engineers of PL Corp working for RCA filed a patent which described the basic principle of using heat in conjunction with a magnetic field to record data. This was followed by many other patents in this area with the initial focus on tape storage.
- In the 1980s, a class of mass storage device called the magneto-optical drive became commercially available which used essentially the same technique for writing data to a disk. One advantage of magneto-optic recording over purely magnetic storage at that time was that the bit size was defined by the size of the focused laser spot rather than the magnetic field. In 1988, a 5.25-inch magneto-optic disk could hold 650 megabytes of data with a roadmap to several gigabytes; a single 5.25" magnetic disk had a capacity of around 100 megabytes.
- In early 2009 Seagate achieved 250 Gb per square inch using HAMR. This was half of the density achieved via perpendicular recording at that time.
- Hard disk technology progressed rapidly and as of January 2012, desktop hard disk drives typically had a capacity of 500 to 2000 gigabytes, while the largest-capacity drives were 4 terabytes. It was recognised as early as 2000  that the then current technology for hard disk drives would have limitations and that heat-assisted recording was one option to extend the storage capacity.
- In March 2012 Seagate became the first hard drive maker to achieve the milestone storage density of 1 terabit per square inch using HAMR technology.
- In October 2012 TDK announced that they had reached a storage density of 1.5 terabit per square inch, using HAMR. This corresponds to 2TB per platter in a 3.5" drive.
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 some capacity point, the bit size is so small and the coercivity correspondingly so high that the magnetic field used for writing data cannot be made strong enough to permanently affect the data and data can no longer be written to the disk. HAMR solves this problem by temporarily and locally changing the coercivity of the magnetic storage medium by raising the temperature above the Curie temperature. Above this temperature, the medium effectively loses coercivity and a realistically achievable magnetic write field can write data to the medium.
HAMR could 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.
- As of 2007, Seagate believed it could produce 300 terabit (37.5 terabyte) Hard disk drives using HAMR technology. Some news sites erroneously reported that Seagate would launch a 300 TB HDD by 2010. Seagate responded to this news stating that 50 terabit per-square-inch density is well past the 2010 timeframe and that this may also involve a combination of Bit Patterned Media.
- In May 2014, Seagate said they planned to produce low quantities of 6 to 10TB capacity hard disks in the "near future", but that this would require "a lot of technical investment as you know, it’s also a lot of test investment". Though Seagate has not stated that the new hard disks would use HAMR, bit-tech.net speculates that they will. Seagate started shipping 8TB drives around July 2014, but without saying how that capacity was reached; extremetech.com speculates that shingled magnetic recording was used rather than HAMR.
- US patent 2915594, BURNS JR., LESLIE L. & KEIZER, EUGENE O., "Magnetic Recording System", published 1959-12-01, assigned to RADIO CORPORATION OF AMERICA
- Seagate ST-41200N
- ca. 2009 - IEEE Spectrum overview article
- Seagate Is The First Manufacturer To Break The Capacity Ceiling With A New 4TB GoFlex Desk Drive
- Kryder, M.H., "Magnetic recording beyond the superparamagnetic limit," Magnetics Conference, 2000. INTERMAG 2000 Digest of Technical Papers. 2000 IEEE International , vol., no., pp. 575, 4–8 April 2005 doi:10.1109/INTMAG.2000.872350
- Seagate Reaches 1 Terabit Per Square Inch Milestone In Hard Drive Storage With New Technology Demonstration
- ca. 2007 - 300 terabit HDDs in the future
- ca. 2007 - No 300TB or 37.5TB HDDs in 2010