EVOLUTION OF BICRYSTAL MEDIA DEVELOPMENT

A general review of studies on microstructure, magnetic properties and recording performance of bicrystal media grown on single crystal subs trates, a NiP/Al substrate and a glass substrate is given, With simila r magnetic properties, a direct experimental comparison of recording p erformance of CoCrPtTa /Cr/NiP films between the media with Cr (200) a nd Cr (110) textures on glass ceramic substrate is provided, Typically , 5-6 dB SNR improvement is observed for medium with Cr (200) texture from recording densities of 40kfci to 140kfci, Medium with Cr (200) te xture has similar to 100 % bicrystal cluster microstructure and has sm aller and more uniform Cr grains. A noise mechanism is discussed that relates the bicrystal microstructure to an effective random anisotropy field magnitude. Micromagnetic simulations show the latter will reduc e medium noise when there is relatively large intergranular exchange c oupling between the grains, However, when the intergranular exchange c oupling is small, the introduction of random anisotropy field magnitud e will increase the medium noise. The other noise mechainsm could be d ue to larger Cr grain size. A bigger magnetic cluster could be formed because more Co alloy grains on a larger Cr grain are coupled together through stronger inner intergranular exchange force, which leads to h igher media noise.