Fluctuation fields and medium noise in CoCrTa and CoCrPt films

The correlation between magnetic viscosity and medium noise in CoCrTa and CoCrPt longitudinal thin-film media was investigated by measuring the time dependence of the remanence coercivity H-r and the read/write characteristics. The media were prepared by de magnetron sputtering under various conditions. Fluctuation fields H-f of the magnetic viscosity at H/H-r=1 were obtained from the slopes of the H-r versus In t plots. The medium noise decreases with kT/H-f (the product of activation volume and saturation magnetization per unit volume), and is independent of other magnetic properties, such as the coercivity and the remanent magnetization per unit area. The medium noise thus primarily depends on the size of the minimum unit of the magnetic moment in reversal.