Magnetic recording: advancing into the future

Abstract

In recent years, the stability of recorded data against thermal decay has become an important criterion for judging the performance of magnetic recording systems. Continued growth of storage densities in the presence of thermally activated behaviour, often called the `superparamagnetic effect', requires new innovations in the recording system in general, and the recording media, in particular. This paper reviews some of the recent advances in recording media (e.g. oriented and antiferromagnetically coupled media) that have helped magnetic recording to maintain the areal density growth rate. However, more innovations and novel architectures are needed for the solutions of tomorrow. Among the more promising media approaches, which are discussed in this paper, are perpendicular, patterned and self-assembled nanoparticle media. Additionally, thermally assisted recording is also reviewed as it combines good writeability with high thermal stability.

Reversal-mechanism of perpendicular switching induced by an in-plane current

“…Compared with conventional spin transfer torques (STTs), they do not need another ferromagnetic layer as a spin polarizer and the high driving current density does not need to cross the tunnel barrier 6,7 . However, there are many debates on the SO torque induced magnetization dynamics, for example, whether the spin Hall torque (SHT) from SHE 4,5 or Rashba effect 3 is the dominant source to induce the magnetic switching.…”

Highly efficient all-optical switching of magnetization in GdFeCo microstructures by interference-enhanced absorption of light

“…Several efficient techniques have already been developed for recording and retrieving nanosize magnetic bits, but the rate of writing and reading single data is still limited to several ns. 1 One way for obtaining a faster working speed together with energyefficient data storage is the use of all-optical switching (AOS) in rare-earth transition metal ferrimagnetic thin films, 2 in which unsurpassed recording rates have been demonstrated. 3,4 The switching process here is ignited by the absorption of photons 5,6 and requires an amount of energy which compares favorably with present-day magnetic recording technologies.…”

Collective states of interacting ferromagnetic nanoparticles

“…A FM nanoparticle is defined as superparamagnetic (SPM), when the energy barrier, E B , for a magnetization reversal is comparable to the thermal energy, k B T, during the measurement. The direction of the superspin then fluctuates with a frequency f or a characteristic relaxation time, τ −1 = 2π f. It is given by the Néel-Brown expression [3], τ = τ 0 exp(KV / k B T ), (1) where τ 0 ∼ 10 −10 s is the inverse attempt frequency, K an effective anisotropy constant and V the volume of the nanoparticle. The energy barrier is here approximated by E B = KV.…”