Effect of diamond types on textured surface morphology and magnetic performance in hard disk

It is well known that hard disk drive media with high orientation ratio (OR) has higher SNR and better thermal stability, which is desirable for higher density recording. The oriented media requires a mechanical texturing process on NiP-plated Al-substrates. Mechanical texturing process is a process to generate circumferential texture patterns (grooves) on the NiP surface using tape with diamond slurry rotating the disk while contacting of the tape and slurry. In this study, we compare the texture parameter δ/λ, where δ is the average depth of the texture line and λ is the average distance between two texture lines, line density (LD), orientation ratio (OR), and recording performances of disks prepared by three types of diamond slurries, namely mono-crystalline diamond (MD), poly-crystalline diamond (PD), and poly-mono-crystalline diamond (Hybrid). Mono-crystalline diamond slurry is a single crystallite, which has sharper edges and fewer facets. Poly-crystalline diamond slurry contains many single crystallites, which has more rounded edges and facets. Hybrid-crystalline diamond is formed from milled (and rounded) mono-crystalline diamond, using atmospheric and temperature changes to micro fracture the surface of the mono-crystallite structure, producing a harder nucleus and more and sharper cutting facets as compared to poly-crystalline diamond. Experimental results show that the substrates textured with hybrid-crystalline diamond slurry can create disk surface with the highest line density and δ/λ, which results in the highest OR, the lowest intergranular exchange coupling energy, the lowest DC erase noise, and the highest SNR, than the substrates textured with mono-crystalline and poly-crystalline diamond slurries. With increasing the texture parameter δ/λ from 0.034 to 0.058, an OR increases from 1.48 to 1.82 and the SNR increases from 19.10 to 19.66. There are very well correlations among δ/λ, OR, and SNR.