Calculation of individual bit island switching field distribution in perpendicular magnetic bit patterned media

Bit patterned media (BPM) is a promising candidate to achieve ultrahigh recording density in magnetic data storage. One of the critical issues for BPM in high-density recording is that the switching field distribution (SFD) needs to be narrow enough to secure exact addressability of individual predefined bits without overwriting adjacent bits. In our work, we observed magnetic reversal of individual islands through magnetic force microscopy and calculated the demagnetization and SFD using the obtained intrinsic SFD to verify if dipole–dipole interactions contribute to the SFD broadening. In simulation, we used the formula in the calculation of critical magnetic field for the reversal of individual islands: Hc = Hc,int − ΣMsVbit/r3, where Hc is the critical field, Hc,int is the initial critical field without dipole–dipole interactions, and Σ represents the dipole–dipole interactions from neighboring islands. Hc,int was generated from the obtained initial SFD (2σ = 1.2 kOe), dipole–dipole interactions cause a significant SFD broadening. The width of 2σ = 1.7 kOe after the calculation with the consideration of the dipole–dipole distribution is in a relatively good agreement with our experimental data (2σ = 2.0 kOe). The calculated demagnetization loop also agrees well with our experimental result.