Thermally induced error: Density limit for magnetic data storage

Abstract

Magnetic data storage is pervasive in the preservation of digital information and the rapid pace of computer development requires ever more capacity. Increasing the storage density for magnetic hard disk drives requires a reduced bit size, previously thought to be limited by the thermal stability of the constituent magnetic grains. The limiting storage density in magnetic recording is investigated treating the writing of bits as a thermodynamic process. A 'thermal writability' factor is introduced and it is shown that storage densities will be limited to 15 to 20 TBit/in 2 unless technology can move beyond the currently available write field magnitudes.PACS numbers: 85.70.Li,75.50.Ss,75.75+a As a technology, magnetic recording has been in existence since the invention of magnetic tape recording in the 1920s and 1930s. Since the early 1980's, and the introduction of metallic thin film recording media, the industry has seen a rapid increase in storage density; up to the TByte storage available in today's PC hard drives. Because technology has kept pace with demand, magnetic information storage is now ubiquitous. Having been around for some 60 years, magnetic recording is running into difficulties imposed by physical limitations.A previous study of the possible limits of recording density was made by Charap et al 1 . This study predicted an upper limit of 36 Gb/in 2 and, remarkably, current technology has already achieved densities over one order of magnitude beyond this value. The reason for this lies in advances in the 'non-magnetic' aspects of recording technology, including error detection and correction and the mechanical actuator systems used to position the read and write sensors, which were not anticipated by the authors of Ref. 1. The question is; does there exist a physical upper limit to recording density which cannot be exceeded by improved technology? Here we argue that the limitation is essentially determined by the maximum tolerable Bit Error Rate and certain materials parameters which, critically, includes the saturation magnetisation of the recording medium.Magnetic recording relies on the storage of information on media comprised of grains of a material with a high magnetocrystalline anisotropy. The grains can be considered as bistable systems capable of representing bits of information in terms of the polarity of the grains. Stability of the information is provided by an anisotropy energy barrier KV where K is the anisotropy constant and V the grain volume. It has long been realised that the phenomenon of 'superparamagnetism' (SPM) defines the upper limit thermal stability of magnetic materials 2 . In the case of magnetic recording information should be stable for at least 10 years, which leads to an established criterion of KV /kT > 60 for media design.Future advances in magnetic recording density will have to circumvent the magnetic recording trilemma 3 .The key component of the trilemma is the necessary reduction in grain size for signal to noise reasons. For thermal stability the anisotropy...

Ultrafast thermally induced magnetic switching in synthetic ferrimagnets

“…In Ref. 23, it was shown that thermal writability is a more important factor than the thermal stability criterion in determining the limiting recording density. The effective field in the TIMS process is the exchange field between the sublattices, which is significantly larger than the values accessible by today's inductive technology, which would essentially remove the thermal writability as a limiting factor in magnetic recording.…”

“…Second, it has been shown that the magnitude of the write field is a major factor limiting the ultimate density in magnetic recording. 23 Essentially, the field during writing must be sufficiently large to overcome thermally driven back-switching of the magnetization, a factor termed the thermal writability. In Ref.…”

Influence of the Ag and Cu Intermediate Layers on the Temperature Ranges of Phase Transformations in Pt/Fe Film Compositions

“…Завдяки набору високих магнетних характеристик, -коерцити-вної сили (27-35 кЕ), магнетування наситу ( 1500 е.м.о./см 3 ), маг-нетокристалічної анізотропії (K u  7·10 6 Дж/м 3 ), -значний інтерес для використання в якості носія магнетного запису з надвисокою щільністю викликають нанорозмірні плівки на основі хемічно впо-рядкованої фази L1 0 -FePt [2][3][4][5].…”

Atomistic simulation of sub-nanosecond non-equilibrium field cooling processes for magnetic data storage applications

“…In combination with the usual requirements for the trilemma, this leads to the magnetic recording quadrilemma, 9 which also places a fundamental limit on the ultimate achievable recording density 10 . For reasonably sized grains (with large µ), the thermal writability is close to one, meaning that given an infinite amount of time the writing process will achieve the thermal equilibrium value of the magnetization defined in Eq.…”

“…Unlike conventional recording, where the applied field initiates deterministic switching of the magnetic state, thermally assisted writing requires that at the writing temperature the applied field is strong enough to overcome the thermal writability to orient the magnetization m, defined by 8,9 m = tanh µ 0 µH k B T wr (1) where µ 0 is the permeability of free space, µ is the magnetic moment, k B is the Boltzmann constant, H is the applied field and T wr is the writing temperature. In combination with the usual requirements for the trilemma, this leads to the magnetic recording quadrilemma, 9 which also places a fundamental limit on the ultimate achievable recording density 10 .…”