Investigation of Dynamic Magnetization in FePt and FePd Disk Ferromagnets Using Micromagnetic Simulation

In this study, we have observed the magnetic hysteresis loop of the highly anisotropic ferromagnetic materials FePt and FePd with disk model by micromagnetic simulation method based on the Landau-Lifshitz-Gilbert (LLG) equation. We used disk shaped model with varied size from 50 to 500 nm, thicknesses of 5 and 10 nm, and damping constant = 0.05. The cell size of 2.5 × 2.5 × 2.5 nm³ was used and the in-plane and out-plane fields were applied to the materials. The results showed that the hysteresis loop has a large coercivity when the external in-plane field and close to zero when the external out-of-plane field was applied. This characteristic was similar as typical of the material's hysteresis loops given the field toward the hard-axis. However, coercivity still observed in materials with size below ≤ 100 nm with ranging values between 20 and 80 mT. From the results, a certain value of the coercivity field appeared in out-plane applied field indicated a perpendicular magnetic anisotropy (PMA) behaviour in FePt and FePd ferromagnets. Moreover, the nucleation field was shifted as the material's size varied. The results showed that the size affected the magnetic properties of the FePt and FePd thin layers.