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The reduction of the transition curvature of written bits in heat-assistedmagnetic recording (HAMR) is expected to play an important role for the futureareal density increase of hard disk drives. Recently a write head design withflipped write and return poles was proposed. In this design a large spatialfield gradient of the write head was the key to significantly reduce thetransition curvature. In this work we optimized the write pole of aheat-assisted magnetic recording head in order to produce large field gradientsas well as large fields in the region of the heat pulse. This is done bytopology optimization. The simulations are performed with dolfin-adjoint. Forthe 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 arecomputed with a coarse-grained Landau-Lifshitz-Bloch (LLB) model and theresulting transition curvature is analysed. Additional simulations with abilayer structure with $50\%$ hard and $50\%$ soft magnetic material arecomputed. The results show that for both recording media, the optimized headdesign does not lead to any significant improvement of the written track. Thus,we analyse the transition curvature for the optimized write heads theoreticallywith an effective recording time window (ERTW) model. Moreover, we check howhigher field gradients influence the curvature reduction. The results show thata simple optimization of the conventional head design design is not sufficientfor effective curvature reduction. Instead, new head concepts will be needed toreduce transition curvature.

Write head design for effective curvature reduction in heat-assisted magnetic recording by topology optimization