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The reduction of the transition curvature of written bits in heat-assisted magnetic recording is expected to play an important role for the future areal density increase of hard disk drives. Recently, a write head design with flipped write and return poles was proposed. In this design, a large spatial field gradient of the write head was the key to significantly reduce the transition curvature. In this work, we optimized the write pole of a heat-assisted magnetic recording head in order to produce large field gradients as well as large fields in the region of the heat pulse. This is done by topology optimization. The simulations are performed with dolfin-adjoint. For the maximum field gradients of 8.1 mT/nm, 8.6 mT/nm, and 11.8 mT/nm, locally resolved footprints of an FePt-like hard magnetic recording medium are computed with a coarse-grained Landau-Lifshitz-Bloch model, and the resulting transition curvature is analyzed. Additional simulations with a bilayer structure with a 50 % hard and 50 % soft magnetic material are computed. The results show, that for both recording media, the optimized head design does not lead to any significant improvements in the written track. Thus, we analyze the transition curvature for the optimized write heads theoretically with an effective recording time window model. Moreover, we check how higher field gradients influence the curvature reduction. The results show that a simple optimization of the conventional head design is not sufficient for effective curvature reduction. Instead, new head concepts will be needed to reduce the transition curvature. [ABSTRACT FROM AUTHOR]

We optimize the recording medium for heat-assisted magnetic recording by using a high/low T c bilayer structure to reduce AC and DC noise. Compared to a former work, small Gilbert damping α = 0.02 is considered for the FePt-like hard magnetic material. Atomistic simulations are performed for a cylindrical recording grain with diameter d = 5 nm and height h = 8 nm. Different soft magnetic material compositions are tested, and the amount of hard and soft magnetic material is optimized. The results show that for a soft magnetic material with α SM = 0.1 and J i j , SM = 7.72 × 10 − 21 J / link , a composition with 50 % hard and 50 % soft magnetic material leads to the best results. Additionally, we analyze how much areal density can be improved by using the optimized bilayer structure compared to the pure hard magnetic recording material. It turns out that the optimized bilayer design allows an areal density that is 1 Tb / in. 2 higher than that of the pure hard magnetic material while obtaining the same signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

It is assumed that heat-assisted magnetic recording 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 Pswitch >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 Pswitch >99.2%, an off-track jitter parameter σoff,80/20=0.46 nm and a down-track jitter parameter &#963down,80/20=0.49 nm. [ABSTRACT FROM AUTHOR]