IEEE TRANSACTIONS ON MAGNETICS, VOL. 52, NO. 2, FEBRUARY 2016 3000606 Writer and Reader Head-to-Media Spacing Sensitivity Assessment in HAMR Chris Rea 1 , Mourad Benakli 1 , Pradeep Subedi 1 , Riyan Mendonsa 1 , Sangita Kalarickal 2 , James Kiely 1 , Weibin Chen 1 , Hua Zhou 1 , Stephanie Hernandez 2 , Yingguo Peng 3 , Jan-Ulich Thiele 3 , Alexander Q Wu 3 , Ganping Ju 3 , Tim Rauch 2 , Kaizhong Gao 2 , Mike Seigler 1 , and Edward Gage 2 1 Recording Head Operations, Seagate Technology, Bloomington, MN 55435 USA 2 Storage Research Group, Seagate Technology, Shakopee, MN 55379 USA 3 Seagate Technology, Fremont, CA 94538 USA We collate multiple experimental measurements of heat-assisted magnetic recording (HAMR) near-field transducer (NFT) and reader sensitivity measurements on spinstand to compare and contrast with the conventional perpendicular magnetic recording (PMR). The readback process shares many similarities, but differences appear due to the increased measured curvature of the prewritten track, which increases the observed pulsewidth (Pw50), lower readback amplitude due to reduced flux from the media transition (MrT), and increased coating thicknesses. We find that the reader head-to-media spacing (HMS) sensitivities and requirements converge toward the conventional scaling requirements. The HAMR write process is more complex due to the uncertainties associated with the optical properties and protrusion position of the NFT. However, accumulating multiple studies varying write HMS with coatings, NFT changes, and media changes, we consistently observe lower sensitivities compared with the conventional writer HMS, in line with modeled comparisons, leading to more relaxed requirements on the NFT clearance than the PMR write HMS. A 1.5 Tbpsi basic technology demonstration demo is shared using the HMS numbers in the bounds of the claims. Index Terms— Basic technology demonstration (BTD) demo, head-to-media spacing (HMS), heat-assisted magnetic recording (HAMR), near-field transducer (NFT). I. I NTRODUCTION W ITH the recent 1.0 Tb/in 2 [1] and 1.4 Tb/in 2 [2] basic technology demonstrations, and drive level demonstration [3], [4], heat-assisted magnetic record- ing (HAMR) [5] has proved to be a viable and promis- ing technology for future magnetic data-storage products. The commercialization of HAMR presents some significant technical challenges that need to be resolved before the wide- spread adoption of the technology can begin. Head-to-media spacing (HMS) has long been a key input for recording scaling. The dependence and sensitivity for new recording technolo- gies must be bounded in order to understand opportunities and risks. In this paper, we compare and contrast the HAMR write and readback processes. The readback process shares simi- larities with the conventional perpendicular magnetic record- ing (PMR) readback process, but it is distinguished by the increased curvature in the HAMR recorded patterns and the increased spacing due to coatings (head and media) and media roughness [6]. Experimental and modeled reader HMS sensitivities are compared at high-density recording conditions with the PMR. Understanding these different characteristics enables us to better project reader HMS requirements for the HAMR system. HAMR relies upon focused energy using near-field plasmonics technology during the write process to elevate the media temperature close to the Curie point [5]. A significant challenge in the HAMR is the definition and control of the writer clearance in the presence of large protrusions [6], Manuscript received July 31, 2015; revised September 4, 2015; accepted September 16, 2015. Date of publication December 9, 2015; date of current version January 18, 2016. Corresponding author: C. Rea (e-mail: chris.j.rea@seagate.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMAG.2015.2483319 Fig. 1. Schematic for the writer and reader HMS factors for the HAMR recording and writer HMS indicated. temporal variation of the thermal expansion [7], and impact of interface materials, including lubricant, on the write process [8], [9]. We explore the influence of the near-field transducer (NFT) clearance control on the recording perfor- mance. HAMR models and measurements are compared in order to better understand the influence of optical spacing versus clearance control. Curvature, jitter, and noise break- down techniques are exploited in order to isolate relative contributions with the write clearance. Using this information, we can bind the NFT design requirements and compare with the recording roadmap requirements [10]. This paper illustrates the HMS requirements with high areal density capability (ADC) by sharing an HAMR basic technology demonstration (BTD) with areal density as high as 1.5 Tb/in 2 , advancing from the 1.3 Tb demo recently shared [2] earlier in the year. As shown in Fig. 1, the definition of HMS shares strong similarities with that of the conventional PMR, differences being the coating choices for the heads, media, and the rough- ness/clearance differences from the choice of FePt HAMR media. The writer HMS is more complex and must account 0018-9464 © 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.