R&D: ReaxFF Molecular Dynamics Study of Mechanochemical Degradation of PFPE Lubricants on DLC in HAMR

RSC Mechanochemistry has published an article written by Himanshu Shekhar, Shota Uchiyama, Yuxi Song, Hedong Zhang, Department of Complex Systems Science, Graduate School of Informatics, Nagoya, University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan, Kenji Fukuzawa, Shintaro Itoh, and Naoki Azuma, Department of Micro-Nano Mechanical Science and Engineering, Nagoya, University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.

Abstract: “Understanding the degradation mechanisms of perfluoropolyether (PFPE) lubricants is critical for the reliability of Heat-Assisted Magnetic Recording (HAMR) systems. In this study, we conducted ReaxFF reactive molecular dynamics simulations to investigate the role of diamond-like carbon (DLC) surfaces in PFPE degradation under confined shear and elevated temperature. The results show that confined shear plays a dominant role than temperature, with the decomposition rate constant increasing with shear velocity. PFPE degradation primarily initiates through C–OH bond rupture at end groups, typically after the OH group bonds to the DLC surfaces. Bonded PFPE molecules adopt bridge and loop conformations, both contributing comparably to degradation with increasing shear velocity, with bridges being slightly more sensitive to shear. Our analysis suggests that bridge dissociation is facilitated by shear-induced end-to-end stretching, while loop dissociation is driven by entanglement of conformationally flexible main chains. These insights provide guidance regarding further development of reliable HAMR systems.“

R&D: Thermal Simulation for Ultrafast Laser in Multilayered Sample for Heat-Assisted Magnetic Recording Application

Baghdad Science Journal has published an article written by Haidar J. Mohamad, and Basaad Hadi Hamza, Department of Physics, College of Science, Mustansiriyah University, Baghdad, Iraq.

Abstract: “Heat-Assisted Magnetic Recording (HAMR) is a promising step in expanding hard disk capacity. This technique depends on the ultrafast laser to demagnetize the layer and record the data on a hard disk or any storage media. However, the recipe for the layers is challenging and gives a space to explore. The investigation of the effects of temperature profile and thermal gradient on the suggested sample FePt (8 nm)/MgO (8 nm)/SiO₂ (58 nm)/Si (9.32 E-7 m) for HAMR use was the focus of this study. The simulation of the multilayered gives a view of ultrafast laser behavior (power density 1.7923 E14 W/m² with an 800 nm wavelength) inside the sample stack. The optical consideration is calculated depending on the incident, reflected, and transmitted light on the surface between layers. Sample layer thickness plays a crucial role in reducing laser power. The temperature gradient inside the sample helps choose the appropriate laser power, which is used with the HAMR technique. Results show the influence of temperature on sample thickness and temperature as laser power. Then, it is obvious which thickness and power laser can be used efficiently.“

R&D: Er-driven Magnetic Tunability in FePt Thin Films Investigated via High-throughput Experiments and Microstructure Analysis for Future HAMR Media

Applied Physics Letters has published an article written by Daisuke Ogawa, National Institute for Materials Science (NIMS), Tsukuba, 305-0047, Japan, Yuma Iwasaki, Center for Basic Research on Materials (CBRM), National Institute for Materials Science (NIMS), Tsukuba 305-0047, Japan, Jun Uzuhashi, Yuta Sasaki, National Institute for Materials Science (NIMS), Tsukuba, 305-0047, Japan, Masato Kotsugi, Department of Materials Science and Technology, Tokyo University of Science, Tokyo 125-8585, Japan, and Yukiko K. Takahashi, National Institute for Materials Science (NIMS), Tsukuba, 305-0047, Japan.

Abstract: “This study undertakes comprehensive experimental validations based on theoretical predictions of the impact of Er and Tm doping on the magnetic properties of FePt thin films. Initial theoretical investigations indicate that doping with rare earth elements may result in promising alterations to the magnetic properties of the FePt thin films, with Er doping in particular offering a promising avenue for further study. Experimental synthesis via a combinatorial high-throughput sputtering system, which enables precise control over the composition of FePt thin films, achieves the desired magnetic properties. Small quantities of dopants, specifically 0.35 at. % Er, substantially enhance the key magnetic properties of saturation magnetization (⁠ μ0Ms⁠), anisotropy constant (⁠ Ku⁠) at room temperature, and the Curie temperature (⁠ TC⁠). Precise microstructural observations of a sample show that Er segregates at grain boundaries, voids, and the substrate/FePt interface, where Er preferentially replaces Fe sites. In other regions of the FePt grains, Er is not solid-soluble, and pure FePt and FePtEr form a composite material in the order of tens of nm. The incorporation of Er also influences the damping constant α⁠. The findings of this study substantiate the intrinsic characteristics of Er-doped films, particularly the enhanced μ0Ms⁠, Ku⁠, and TC attainable with nominal dopant concentrations, and facilitate the realization of ultimate magnetic recording densities anticipated for future data storage technologies.“