SNR Enhancement in Segmented Perpendicular Media

In this paper, we present a systematic micromagnetic modeling investigation on the segmented perpendicular thin film media. Segmented medium with inserted exchange breaking layers not only enables tunability of the crystalline anisotropy at each segment through the medium thickness, but also enables a continuous tuning of the inter-segment ferromagnetic exchange coupling strength. It is found that the switching field distribution can be significantly narrowed by optimizing the inter-segment coupling. This is because for a three-segment grain, the switching field dependence on the anisotropy field variation of the segment with highest anisotropy field can be substantially suppressed with adequate inter-segment coupling. Recording simulation shows that optimizing the inter-segment coupling strength combined with the optimization of anisotropy field for each segment, significant SNR enhancement can be achieved. Although optimizing the inter-segment coupling does yield reduction of the energy barrier, it also reduces the switching field in proportion, such that the anisotropy strength can be engineered with sufficient thermal stability. It is argued that as long as the grain size is smaller than half of the bit length, segmenting the medium grains presents an alternative and likely more effective approach than that of reducing the grain size for increasing the area density capability.