Evolution of bicrystal media development

A general review of studies on microstructure, magnetic properties and recording performance of bicrystal media grown on single crystal substrates, a NiP/AI substrate and a glass substrate is given. With similar magnetic properties, a direct experimental comparison of recording performance of CoCrPtTa /Cr/NiP films between the media with Cr (200) and 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) texture has ~100 % bicrystal cluster microstructure and has smaller 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 reduce medium noise when there is relatively large intergranular exchange coupling between the grains. However, when the intergranular exchange coupling is small, the introduction of random anisotropy field magnitude will increase the medium noise. The other noise mechainsm could be due 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 higher media noise.