Simulation of Heat Assisted Magnetic Recording System

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Simulation of Heat Assisted Magnetic Recording System

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2018-11

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Heat-assisted magnetic recording (HAMR) is a promising approach to increase the areal density of hard disk drives (HDDs). The first part (Chapter 2~3) of this dissertation provides a computational framework/program for HAMR simulation and a system-level optimization is then discussed in the second part (Chapter 4~6). Anisotropic exchange has been incorporated in a description of magnetic recording media near the Curie temperature, as would be found during HAMR. The new parameters were found using a cost function that minimized the difference between atomistic properties and those of renormalized spin blocks. Interestingly, the anisotropic exchange description at 1.5 nm discretization yields very similar switching and magnetization behavior to that found at 1.2 nm (and below) discretization for the previous isotropic exchange. This suggests that the increased accuracy of anisotropic exchange may also reduce the computational cost during simulation. We then studied several factors that could affect the playback signal-to-noise ratio (SNR), such as the switching time of the writing field, the peak temperature of the heat spot, the standard deviation of anisotropy field and exchange parameters, and the size of the reader element. We found that bit length (BL) becomes the key factor for the value of SNR for small, e.g., 10 nm, BLs. We established a relationship between the SNR and the bit error rate (BER) so that it will be easy to predict the storage capacity based on the playback SNR. The capacity prediction is performed with current technologies as well as those expected to be available in the near future, since the ultimate user storage-area density for heat-assisted magnetic recording is an important consideration both from research and commercial perspectives. Micromagnetic shows a result of 1.8 Tb/in2. Optimization of track pitch in the absence of track misregistration increases the density to 5 TBit/in2 for perfect recording. Finally, transition noise and remanence noise are the two most important types of media noise in HAMR. We examine two methods (spatial splitting and principal components analysis) to distinguish them: both techniques show similar trends with respect to applied field and grain pitch (GP). It was also found that PW50 can be affected by GP and reader design but is almost independent of write field and bit length (larger than 50 nm). Interestingly, our simulation shows a linear relationship between jitter and PW50NSRrem, which agrees qualitatively with experimental results.

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University of Minnesota Ph.D. dissertation. November 2018. Major: Electrical/Computer Engineering. Advisor: Randall Victora. 1 computer file (PDF); xiv, 115 pages.

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Jiao, Yipeng. (2018). Simulation of Heat Assisted Magnetic Recording System. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/202187.

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