Lowering HAMR Near-Field Transducer Temperature via Inverse Electromagnetic Design

Bhargava, Samarth; Yablonovitch, Eli

doi:10.1109/tmag.2014.2355215

Cited by 38 publications

(25 citation statements)

References 13 publications

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“…However, as pointed out in a series of recent studies on the thermal stability of these NFTs [8–11], they are inherently sensitive to thermal degradation under the suggested operating conditions, and current SPR designs might not be able to satisfy the requirement of highly reliable HDDs which have to operate for several years under high load. In addition, current designs feature a magnetic writing tip being laterally displaced by several nanometers from the SPR due to implementation requirements [12], i.e., the recording medium is heated first and only subsequently magnetized.…”

Section: Introductionmentioning

confidence: 99%

Grazing-incidence optical magnetic recording with super-resolution

Scheunert¹,

Cohen²,

Kullock³

et al. 2017

Beilstein J. Nanotechnol.

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Heat-assisted magnetic recording (HAMR) is often considered the next major step in the storage industry: it is predicted to increase the storage capacity, the read/write speed and the data lifetime of future hard disk drives. However, despite more than a decade of development work, the reliability is still a prime concern. Featuring an inherently fragile surface-plasmon resonator as a highly localized heat source, as part of a near-field transducer (NFT), the current industry concepts still fail to deliver drives with sufficient lifetime. This study presents a method to aid conventional NFT-designs by additional grazing-incidence laser illumination, which may open an alternative route to high-durability HAMR. Magnetic switching is demonstrated on consumer-grade CoCrPt perpendicular magnetic recording media using a green and a near-infrared diode laser. Sub-500 nm magnetic features are written in the absence of a NFT in a moderate bias field of only μ0 H = 0.3 T with individual laser pulses of 40 mW power and 50 ns duration with a laser spot size of 3 μm (short axis) at the sample surface – six times larger than the magnetic features. Herein, the presence of a nanoscopic object, i.e., the tip of an atomic force microscope in the focus of the laser at the sample surface, has no impact on the recorded magnetic features – thus suggesting full compatibility with NFT-HAMR.

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Section: Introductionmentioning

confidence: 99%

Grazing-incidence optical magnetic recording with super-resolution

Scheunert¹,

Cohen²,

Kullock³

et al. 2017

Beilstein J. Nanotechnol.

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“…By reducing the required computation from N to 2, this method can be orders of magnitude more computationally efficient. A rigorous mathematical derivation of the adjoint method applied to freeform boundaries in electromagnetics has been described elsewhere [7], [10]. Briefly, there are two key concepts in the qualitative explanation of calculating the gradient in electromagnetics in only 2 simulations.…”

Section: Adjoint Methods Via Lorentz Reciprocitymentioning

confidence: 99%

“…Since there is very little electric field at the center of the NFT, the combined heatsink-NFT structure does not overtly deviate in electromagnetic behavior from that of a typical thin film lollipop NFT. The narrowness of the cylindrical heatsink limits the heat conduction out of the NFT peg and is major bottleneck towards increasing the media/NFT temperature ratio [10].…”

Section: Mock Industry Systemmentioning

confidence: 99%

“…The bulk gold layer in the fat NFT not only acts as an aggressive heatsink but also significantly affects the NFT's electromagnetic behavior. Hence, a typical PSIM may mode-match to the lollipop NFT but does not mode-match to the fat NFT [10]. Nonetheless, the fat NFT can indeed focus light into a hotspot on the media with dimensions defined by the NFT peg as long as the incoming illumination mode-matches to it.…”

Section: Proposed Systemmentioning

confidence: 99%

“…Since heuristic algorithms like particle swarm and genetic algorithms rely on random trials, they are too computationally burdensome for practical engineering design for optics in the nano-scale. In contrast, the Inverse Electromagnetic Design software performs gradient-based optimization using the adjoint method, which results in fast deterministic optimization that is computationally inexpensive [7]- [10].…”

Section: Introductionmentioning

confidence: 99%

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Multi-objective inverse design of sub-wavelength optical focusing structures for heat assisted magnetic recording

Bhargava

Yablonovitch

2014

SPIE Proceedings

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We report using Inverse Electromagnetic Design to computationally optimize the geometric shapes of metallic optical antennas or near-field transducers (NFTs) and dielectric waveguide structures that comprise a sub-wavelength optical focusing system for practical use in Heat Assisted Magnetic Recording (HAMR). This magnetic data-recording scheme relies on focusing optical energy to locally heat the area of a single bit, several hundred square nanometers on a hard disk, to the Curie temperature of the magnetic storage layer. There are three specifications of the optical system that must be met to enable HAMR as a commercial technology. First, to heat the media at scan rates upward of 10 m/s, ~1mW of light (>1% of typical laser diode output power) must be focused to a 30nm×30nm spot on the media. Second, the required lifetime of many years necessitates that the nano-scale NFT must not over-heat from optical absorption. Third, to avoid undesired erasing or interference of adjacent tracks on the media, there must be minimal stray optical radiation away from the hotspot on the hard disk. One cannot design the light delivery system by tackling each of these challenges independently, because they are governed by coupled electromagnetic phenomena. Instead, we propose multiobjective optimization using Inverse Electromagnetic Design in conjunction with a commercial 3D FDTD Maxwell's equations solver. We computationally generated designs of a metallic NFT and a high-index waveguide grating that meet the HAMR specifications simultaneously. Compared to a mock industry design, our proposed design has a similar optical coupling efficiency, ~3x improved suppression of stray optical radiation, and a 60% (280°C) reduction in NFT temperature rise. We also distributed the Inverse Electromagnetic Design software online so that industry partners can use it as a repeatable design process.

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