Energy-assisted magnetic recording (EAMR) is thought to solve the trilemma by improving writability and enhancing areal recording density 1, 2. On the other hand, servo signal writing time, which takes a few days per one drive on manufacturing process, is one of serious problems for high areal recording density in hard disks. Magnetic printing is a strong candidate for servo track writing with extremely high speed and low cost. A new master structure, herein called double magnet master (DMM) medium, was recently proposed for magnetic printing to improve printing characteristics onto EAMR media 3, 4. However, the detailed combination of double magnets to further improve printing characteristics, has not been clarified yet. In this study, the micromagnetic simulation has been carried out in order to reveal an appropriate combination of magnets in DMM.
The conventional single magnet master media were proposed by our previous reports 5, 6. The magnetic pattern in the conventional master media is a soft single magnet (SSM) of FeCo or a single hard magnet (HSM) of CoPt. Thus, the DMM can be expected to utilize two kinds of magnet combinations such as soft-hard double magnet (SDM) and (semi-)hard-hard double magnet (HDM). The recording field distribution and the printed magnetization were calculated by utilizing micromagnetic simulation 3. The recording media consists of hexagonal grain with diameter of 4.6 nm and has the coercivity of 10kOe. The magnetizations printed by 4 kinds of master were shown in Fig. 1. The printed magnetic pattern is L/S with the same pattern width of 10nm corresponding to the bit length. The upper panels of each magnetization distribution of Fig. 1 schematically shows 4 kinds of combinations of magnets. SDM and HDM can clearly print the L/S pattern better than SSM and HSM. Moreover, the SDM has better printing characteristics than that of HDM. The SDM has the FeCo pattern with large magnetization to enhance the recording field, which is larger than that of CoPt in HDM during the application of printing field more than about 8kOe. Therefore, the SDM master is more adequate for magnetic printing onto EAMR media.
References:
1 M. H. Kryder et al., "Heat assisted magnetic recording", Proc. IEEE, vol. 96, no. 11, pp. 1810-1835 (2008).
2 J.-G. Zhu, X. Zhu and Y. Tang, "Microwave assisted magnetic recording", IEEE Trans. Magn., vol. 44, no. 1, pp. 125-131 (2008).
3 T. Komine, "Master structure dependence of double magnet master on performance of magnetic printing onto energy-assisted magnetic recording media", IEEE Trans. Magn. (2022) Early access. DOI: 10.1109/TMAG.2022.3147910
4 T. Komine, "Double magnet master media for magnetic printing onto energy-assisted magnetic recording media", IEEE Trans. Magn. Vol. 58, 3200105 (2021).
5 T. Komine, T. Murata, Y. Sakaguchi and R. Sugita, " Feasibility of perpendicular magnetic printing at 1Tb/in2 ", IEEE Trans. Magn., vol. 44, no. 11, pp. 3416-3418 (2008).
6 N. Sheeda, M. Nakazawa, H. Konishi, T. Komine and R. Sugita, "Perpendicular anisotropy master medium in magnetic printing for writing high-density servo signal", IEEE Trans. Magn., vol. 45, no. 10, pp. 3676-3678 (2009).

Fig.1 Magnetization distribution of printed by 4 kinds of master media.