Lowering HAMR Near-Field Transducer Temperature via Inverse Electromagnetic Design

Heat-assisted magnetic recording (HAMR) allows for data writing in hard disks beyond 1 Tb/in2 areal density, by temporarily heating the area of a single bit to its Curie temperature. The metallic optical antenna or near-field transducer (NFT), used to apply the nanoscale heating to the media, may self-heat by several hundreds of degrees. With the NFT reaching such extreme temperatures, demonstrations of HAMR technology experience write-head lifetimes that are orders of magnitude less than that required for a commercial product. Hence, heating of the NFT is of upmost importance. In this paper, we first derive fundamental limits on the temperature ratio NFT/Media to drive NFT design choices for low-temperature operation. Next, we employ inverse electromagnetic design software, which solves for unexpected geometries of the NFT and waveguide. We present computationally generated designs for the waveguide feeding the NFT that offer a 50 % reduction in NFT self-heating (∼220 °C) compared with typical industry designs. Index Terms — Adjoint method, computational electromagnetics, gradient methods, hard disks, heat-assisted magnetic recording (HAMR), inverse problem, nanophotonics, near-field transducer (NFT), optical antenna, optimization, plasmonics, thermal management. I