Noise reduction in heat-assisted magnetic recording of bit-patterned media by optimizing a high/low Tc bilayer structure

Abstract

It is assumed that heat-assisted magnetic recording (HAMR) is the recording technique of the future. For pure hard magnetic grains in high density media with an average diameter of 5 nm and a height of 10 nm the switching probability is not sufficiently high for the use in bit-patterned media. Using a bilayer structure with 50% hard magnetic material with low Curie temperature and 50% soft magnetic material with high Curie temperature to obtain more than 99.2% switching probability, leads to very large jitter. We propose an optimized material composition to reach a switching probability of P switch > 99.2% and simultaneously achieve the narrow transition jitter of pure hard magnetic material. Simulations with a continuous laser spot were performed with the atomistic simulation program VAMPIRE for a single cylindrical recording grain with a diameter of 5 nm and a height of 10 nm. Different configurations of soft magnetic material and different amounts of hard and soft magnetic material were tested and discussed. Within our analysis, a composition with 20% soft magnetic and 80% hard magnetic material reaches the best results with a switching probability P switch > 99.2%, an off-track jitter parameter σ off,80/20 = 14.2 K and a down-track jitter parameter σ down,80/20 = 0.49 nm.

Improving the signal-to-noise ratio for heat-assisted magnetic recording by optimizing a high/low Tc bilayer structure

“…This result differs from the optimized material composition in Ref. [21], where the optimal composition consists of 80% hard magnetic and 20% soft magnetic materials. In Figure 4, a switching probability phase diagram of the optimized bilayer structure with 50% hard and 50% soft magnetic material can be seen.…”

“…A work to reduce noise in recording media by optimizing a high/low T c bilayer structure (see Ref. [21]) showed that an optimial bilayer structure consists of 80% hard magnetic and 20% soft magnetic material. However, in the former work the Gilbert damping was assumed to be α HM = 0.1 which is hard to achieve in a FePt like hard magnetic material in reality.…”

Curie temperature modulated structure to improve the performance in heat-assisted magnetic recording

“…This material configuration can be seen in Figure 1(a) and was already studied in former works. [9][10][11] Secondly, a grain consisting of two identical layers FePt is considered where the only difference is the peak temperature of the applied heat pulse. Hereby, the peak temperature of the heat pulse applied to the top layer is assumed to be 20% larger than that applied to the bottom layer (see Figure 1(b)).…”

Systematic parameterization of heat-assisted magnetic recording switching probabilities and the consequences for the resulting SNR

“…P max and σ d are clearly two parameters with significant impact on the SNR, so it is recommendable to consider those values in terms of material optimization as in Ref. [5]. Furthermore the variation of two parameters simultaneously lead to SNR contours as in Fig.…”

“…In Ref. [5] for instance, the shape of the phase diagram depending on the composition of a bilayer material is investigated. This information only refers to a single grain but a priori tells very little about the resulting SNR of the read-back signal of a bit series.…”