Upper Limit of Carbon Concentration in Ferromagnetic L1₀-Ordered FePt-C for Tb/in² Data Storage Density Heat-Assisted Magnetic Recording Media

• Published in: IEEE transactions on magnetics 2021-10, Vol.57 (10), p.1-6
• Main Authors: Choi, Minyeong, Hong, Yang-Ki, Won, Hoyun, Mankey, Gary J., Yeo, Chang-Dong, Shah, Nayem M. R., Lee, Woncheol, Jung, Myung-Hwa, Thiele, Jan-Ulrich
• Format: Article
• Language: English
• Subjects: Brillouin function; Carbon; FePt-C; first-principles calculation; Heat-assisted magnetic recording; heat-assisted magnetic recording (HAMR); Iron; Magnetic properties; Magnetic recording; Media; Perpendicular magnetic anisotropy
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/TMAG.2021.3079188

In high-density magnetic recording media, magnetically isolated grains are required to increase the signal-to-noise ratio (SNR). Carbon can be used to isolate FePt grains enabling their grain size smaller than 4.3 nm. Carbon atoms segregate to the boundaries during growth and provide an exchange-breaking layer, however, some other carbon atoms remain dissolved in the magnetic alloy. To identify the upper limit of carbon concentration in L 1_{0} -ordered (Fe 0.5 Pt 0.5 ) 100- x C x , 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/in 2 heat-assisted magnetic recording (HAMR) media and beyond. The calculated magnetization ( M_{s} ) of L 1_{0} -ordered (Fe 0.5 Pt 0.5 ) 100- x C x decreases to 770 emu/cm 3 at x =20 from 1030 emu/cm 3 at x = 0 at 300 K, and the magnetocrystalline anisotropy constant ( K_{u} ) to 2.05 MJ/m 3 at x =20 from 15.48 MJ/m 3 at 300 K. It is striking to find that the Curie temperature ( T_{C} ) 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 M_{s} and K_{u} at 300 K with T_{C} , the M_{s} - K_{u} -