The purpose of the present study is to develop a CoCr type perpendicular medium for ultrahigh density beyond $10Gbit/inch^2$. For this goal, changes of magnetic and microstructural properties of CoCr recording layers deposited on Ti underlayer were systematically studied by varying additive elements in the magnetic layers and by modifying the glass substrate surface with pre-deposition of a paramagnetic and amorphous CoZr layer.
In the first part, the optimum sputter deposition conditions and Cr content were studied in CoCr/Ti bilayer system. It was found that $\Delta \theta_{50}$ of CoCr (00.2) peak decreased with increasing Cr content, decreasing substrate temperature and decreasing sputter pressure for a fixed Ti underlayer thickness of 900Å. $\Delta \theta_{50}$ of CoCr (00.2) peak linearly decreased with increasing Ti underlayer thickness and became a constant at the thickness of 900Å or thicker.
In the second part, effects of third elements such as Ta, Nb, Pt, Hf, Zr and W on Hc and Ms of $(Co_{81}Cr_{19})_{100-X}M_X$ were studied. It was found that Pt was very effective in increasing Hc up to 15at% but Ms decreased slightly with increasing Pt content. Ta was effective in increasing Hc up to 4at% but Ms decreased rapidly. Moreover, Ta was effective in isolating magnetic exchange interaction among CoCr grains. $\Delta \theta_{50}$ were not glass substrates. Although the lattice parameter 'a' has increased by addition of Pt or Ta in CoCr system and lattice parameter 'a' difference of CoCrPt and Ti were slightly reduced, $\Delta \theta_{50}$ did not decreased than CoCr/Ti system.
In the third part, effects of paramagnetic and amorphous $Co_{55}Zr_{45}$ underlayer on magnetic and structural properties of CoCrPt/Ti layer were studied. After pre-deposition of the CoZr underlayer on glass substrates, Ti and CoCrPt layers were deposited sequently with varying Ti layer thickness without breaking vacuum. By the pre-deposition of the CoZr underlayer, magnetic properties of CoCrPt layer were greatly improved even at 100Å Ti thickness. Specifically, perpendicular coercivity was increased to 3000Oe and in-plane coercivity was reduced to 600Oe. It was found that when CoZr layer was deposited, surface roughness was greatly reduced compared with that of the bare glass surface and oxygen level of the surface was also greatly reduced. By these two effects, homogeneous nucleation of randomly oriented Ti nuclei was ensured and Ti grains with (00.2) plane parallel to substrate surface which has lowest surface energy grew selectively during growth process. When strong Ti (00.2) texture developed at a thinner Ti thickness. Ti grain size was small and CoCrPt grain size which grow heteroepitaxy on Ti grain was also small.
In the last part, the most interesting and significant phenomenon of this research will be reported. When the thickness of CoCrPt layer was less than 200Å in CoCrPt/Ti or CoCrPt/Ti/CoZr layers, M-H loop showed a unique behavior. After saturation when applied field was reduced to zero and even a negative field was applied, M value maintained the saturation value. The shape of the M-H loop was similar to Co/Pt or Co/Pd multilayer films. This indicates magnetic crystalline anisotropy, Ku of the Co alloy was increased significantly. The lattice image by high resolution TEM showed 'a' parameter of Co lattice has expanded to that of Ti lattice, which corresponds to more than 15% increase. However, when the CoCrPt thickness increased more than 300Å, an amorphous type layer was formed at the interface of Ti and CoCrPt and lattice parameter 'a' of Co alloy returned to its original value and $K_u$ returned to the normal value of CoCrPt.
The more detailed analyses were discussed. The implication of this finding is that the CoCrPt/Ti perpendicular media can be used ultrahigh density recording for next generation.
