The history of magnetic recording dates back over a century and is driven by the interactions between an external field and a magnetic material. Magnetic recording technology was practically applied to the fabrication of hard disk drives in 1956, and increases in data storage density have spanned eight orders of magnitude in the last 50 years. As a result of these tremendous advances, the placement of hard drives is ubiquitous: routine applications include servers, desktop computers, laptops, digital video recorders, game consoles, video cameras, and so on.
This remarkable progress has been enabled by advances in the coating of thin magnetic films having characteristic grain sizes as small as 7nm. The individual grains, typically made of a material such as CoCrPt for perpendicular recording, are separated from one another by an oxide that forms at the grain boundaries. A cluster of grains with similar magnetization make up a single bit of stored data; many adjacent grains are required to form a volume that is large enough to be precisely “written” and “read” by the head element of a disk drive. In recent years, improvements in bit storage density have been driven by the development of deposition techniques that are capable of producing films with smaller magnetic grains. However, the superparamagnetic effect will eventually limit this progression. Smaller grains eventually become magnetically unstable and the likelihood of a grain spontaneously flipping increases – ultimately resulting in the loss of stored data. The practical limitations of the superparamagnetic effect can be avoided by patterning the boundaries between the magnetic domains, thus the development of patterned media.
