Switching Probability Distribution of Bit Islands in Bit Patterned Media

In this paper, we report magnetic force microscopy (MFM) observations of switching probability of individual bit islands in bit patterned media. The switching probability (p) of each island was measured by repeated reversal tests at the same experimental conditions for each switching field (SF). It was found that there are similar to 60% of islands with 0 < p < 1 for SF = 11 kOe kOe (which is approximately the average remnant coercivity, Hcr of the patterned islands) while the rest of the islands are either switched every time (for magnetically softer islands) or never switched (for magnetically harder islands). The observed statistical behavior of 0 < p < 1 is an indication of thermal fluctuation during switching when magnetostatic energy (due to the applied external field) is comparable to magnetic anisotropy energy. As SF is decreased or increased away from Hcr (11 kOe to 9.5 kOe or 11 kOe to 12.5 kOe), percentage of islands with 0 < p < 1 becomes smaller [narrower switching probability distribution (SPD)], due to less dipolar interaction/variations among islands [which also lead to less switching field distribution (SFD) broadening]. Our results provide insights on the effects of statistical switching behavior of bit islands on the write errors in bit patterned media recording.