Curvature Change of Heat Assisted Magnetic Recording Patterns with Different Bit Lengths

Abstract

Heat assisted magnetic recording (HAMR) has become a very promising candidate for next-generation information storage technology. As recording bit lengths decrease down near ten nanometers in order to further increase the storage density, the recording performance (mainly the signal to noise ratio) cannot satisfy demands. In this study, a new method to characterize the recording pattern quality has been proposed in order to better understand the observed change in performance and help provide improved HAMR designs. In this method, for a given bit length (21nm, 15nm, and 10.5nm), more than 100 recording bit patterns are written micromagnetically, summed and averaged, generating a pattern contour with a crescent shape (Figure 1). This shape is due to the circular shape of the moving heating spot. A single tone binary sequence is used. Thermal Exchange-Coupled Composite media is used, where a moderate anisotropy material serves as the writing layer and an FePt layer serves as the storage layer [1]. By fitting the convex arm of the contour to a parabolic function, the curvature of the contour can be quantified (Figure 2): 10.5nm: 0.0184 (DC) and 0.0178(AC); 15nm: 0.0198 (DC) and 0.0189(AC); 21nm: 0.0222 (DC) and 0.0204(AC) (nm-1). The results show that smaller bit length gives a contour with lower curvature, which means that the recording patterns are less affected by the heat spot shape, less overlapping with each other and better separated. AC-erased media show even smaller curvatures than their DC-erased counterparts, suggesting that AC-erased media could provide better performance.