Effect of Nb content on the microstructure and magnetic properties of CoCrPtNb/CrTi/C thin films

In this study, CrTi, (Co68Cr15Pt17)100−xNbx (x = 0-3.6) multilayers and carbon overcoat were sequentially deposited on glass substrate as underlayer, granular media layer and protective layer, respectively, by rf magnetron sputtering. The effects of Nb added to CoCrPt magnetic layer on the magnetic properties and microstructure of CoCrPtNb thin film media have been examined. As a result, we found that the change in c-axis orientation of CoCrPtNb from out-of-plane to in-plane enhanced Hc, S and S* as the Nb content increases up to 1.5 at.%. Further increase of Nb content decreases the coercivity. This phenomenon may be interpreted as being due to an increase in granular exchange coupling, which is due to a degraded grain-boundary structure. AFM revealed that the width of this boundary phase tended to become thinner with Nb content when Nb content was above 1.5 at.%. At the same time, it is suggested that high-performance CoCr-based recording media can be fabricated at room temperature even when using an isotropic glass substrate by adding moderate amounts of Nb and using a multilayer thin film structure.