Dependence of optical laser power on disk radius, head-disk spacing and media properties in heat-assisted magnetic recor
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TECHNICAL PAPER
Dependence of optical laser power on disk radius, head-disk spacing and media properties in heat-assisted magnetic recording Tan D. Trinh1,2 • Sukumar Rajauria2 • Robert Smith2 • Erhard Schreck2 • Qing Dai2 • Frank E. Talke1 Received: 21 December 2019 / Accepted: 12 May 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In heat-assisted magnetic recording, minimization of optical laser power is important for the reliability of the head-disk interface. In this paper, a prototype heat-assisted magnetic recording system is used to investigate the relationship between the needed optical laser power and disk drive design parameters. In particular, the change of optical laser power, which is a function of the laser current, is investigated for different disk radii and write head flying heights while keeping the write width of the recorded signal constant. In addition, the dependence of laser power during writing is studied as a function of the thickness and material properties of a very thin ‘‘capping layer’’ on the top of the recording magnetic layer. The results show that laser power and media design parameters play a crucial role in heat-assisted magnetic recording devices.
1 Introduction Heat-assisted magnetic recording is a new technology that has the potential to improve the areal density of hard disk drives (HDDs) to 10 Tbit/in2 (Marchon et al. 2013; Challener et al. 2009; Stipe et al. 2010; Kryder et al. 2008). To achieve areal densities as high as 10 Tbit/in2, the magnetic grain volume on the recording medium must decrease to maintain an adequate signal-to-noise ratio (SNR). Decreasing the magnetic grain volume leads to instability of the recorded data on the media surface due to thermal fluctuations, which is described as the ‘‘superparamagnetic’’ phenomenon (Kryder et al. 2008). To overcome this instability, new materials of high anisotropy and high coercivity have been investigated, such as, FePt, CoPt, CoPd, SmCo5, and Nd2Fe14B (Kryder et al. 2008; O’Grady and Laidler 1999; Kief and Victora 2018). However, for these materials, the magnetic field from a conventional write pole is not sufficient to polarize the magnetic film accordingly. In heat-assisted magnetic recording a nanometer-sized area on the disk surface is heated to near or beyond the Curie temperature (TC) of approximately & Frank E. Talke [email protected] 1
Center for Memory and Recording Research, University of California, San Diego, CA, USA
2
Western Digital Corporation, Great Oaks Pkwy, San Jose, CA, USA
450 °C by using optical near-field coupling effects (Challener et al. 2009). At the Curie temperature, the coercivity of the magnetic layer is reduced to zero, which then allows to write data with the magnetic field produced by state-ofthe art magnetic writer. To deliver power from a laser diode mounted on the top of the slider, a plasmonic optical device, ‘‘near-field transducer’’ (NFT), located on the slider air-bearing surface is used. Controlling the
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