A near field transducer (NFT) is a key component for heat-assisted magnetic recording (HAMR). The lollipop design and its variations have had success in HAMR recording systems employed in hard disk drives 1. The designed mode resonance, or mode beating, results in excellent coupling between optical light and the excitation of plasmonic current in the NFT. However, the resonant plasmonic oscillation also yields substantial heating, bringing reliability challenges. In addition, such a resonant design can make the plasmonic excitation of media grains highly dependent on the spacing between the NFT recording peg and the grains in the media. In this paper, we present a design analysis for a novel NFT using a nanocomposite structure to create distributed optical feedback (DFB) for maintaining plasmonic resonance. Figure 1 shows a schematic view of the design. The NFT is made of an array of Au rectangular rods, each separated by a constant gap, G, of nanometer dimension and the Au rods are embedded in a dielectric material. The insert in the figure shows the 2D COMSOL simulation results of the optical field intensity at the peg end of the NFT with W=660nm and G=5nm. For this structure, the optimal free-space optical wavelength λ=710nm. The 2μm long DFB Au nanocomposite has an optical coupling efficiency of 30% with very little field intensity decay at the peg end. Figure 2 shows the calculated electric field intensity in the dielectric gap before the last rod as a function of the width of the Au rods for different gap spacing. In conclusion, the DFB Au nanocomposite NFT design enables enhanced material stability, hence, enhancing the NFT reliability. Plasmonic excitation of medium grains by the NFT has also been modeled and the analysis of its sensitivity to the spacing between the NFT and medium grain will be presented.
1 W.A. Challener, et al, Nature Photonics, 3 (4), 220-224 (2009). 2 K. Shimazawa, W. Xu, K. Fujil, US11,315,591B1, Headway Technologies, (2022)
Fig.1 Schematic view of the distributed feedback Au nanocomposite NFT design. The insert shows the simulation results of optical field intensity inside the dielectric gaps along the 2μm long NFT. The optical wavelength is optimal at λ=710 nm.
Fig.2. Optimization of the DFB Au nanocomposite NFT for Different Au rod width and dielectric gap. The electric field is measured at the end of 2μm long NFT.