R&D: Upper Limit of Carbon Concentration in Ferromagnetic L10-Ordered FePt-C for Tb/in2 Storage Density HAMR Media

IEEE Transactions on Magnetics has published an article written by Minyeong Choi, Yang-Ki Hong, Hoyun Won, Department of Electrical and Computer Engineering, The University of Alabama, Tuscaloosa, AL 35487, USA, Gary J. Mankey, Department of Physics and Astronomy, The University of Alabama, Tuscaloosa, AL 35487, USA, Chang-Dong Yeo, Nayem M. R. Shah, Department of Mechanical Engineering, Texas Tech University, Lubbock, TX 79409, USA, Woncheol Lee, Department of Electrical and Computer Engineering, The University of Alabama, Tuscaloosa, AL 35487, USA and Samsung Electro-Mechanics, Co. Ltd., Suwon, South Korea (Republic of Korea), Myung-Hwa Jung, Departmernt of Physics, Sogang University, Seoul, South Korea (Republic of Korea), and Jan-Ulrich Thiele, Seagate Technology LLC, Fremont, CA 94538 USA.

Abstract: “In high-density magnetic recording media, magnetically-isolated grains are required to increase signal-to-noise ratio (SNR). Carbon can be used to isolate FePt grains enabling their grain size smaller than 4.3 nm. Carbon atoms segregates to the boundaries during growth, and provides an exchange-breaking layer, however, some other carbon atoms remain dissolved in the magnetic alloy. To identify the upper limit of carbon concentration in L10-ordered (Fe0.5Pt0.5)100-xCx, first-principles calculations are performed based on the density functional theory (DFT). The Brillouin function and Callen-Callen empirical relation determine the temperature-dependent magnetization and magneto-crystalline anisotropy energy enabling the determination of magnetic properties and Curie temperature required by 4 Tb/in2 HAMR media and beyond. The calculated magnetization (Ms) of L10-ordered (Fe0.5Pt0.5)100-xCx decreases to 770 emu/cm3 at x = 20 from 1,030 emu/cm3 at x = 0 at 300 K, and the magnetocrystalline anisotropy constant (Ku) to 2.05 MJ/m3 at x = 20 from 15.48 MJ/m3 at 300 K. It is striking to find that the Curie temperature (TC) increases to 728 K at x = 20 from 719 K at x = 0. Regardless of carbon concentration, the magnetic anisotropy direction is the out-of-plane. Combining Ms and Ku at 300 K with TC, the Ms-Ku-C concentration relation is plotted to guide the design of L10-ordered Fe-Pt film for Tb/in2 recording media. It is found that the upper limit of carbon concentration is determined to be about 12 at.% to retain Ms ≥ 800 emu/cm3, TC ≥ 430 K, and Ku ≥ 5 MJ/m3, which are necessary to achieve areal densities of 4 Tb/in2 and beyond.“