A new method for intrinsic viscosity measurements on perpendicular recording media

Summary form only given. In the case of perpendicular media, it is hard to measure the magnetic viscosity S (from the relaxation curve) because the internal field (H/sub 1/) is continuously changing with time due to the change in the demagnetizing field. Correction for this effect using an analytical formula fails in principle to provide accurate results in case S varies largely with field. In this paper, we introduce a new method that allows to measure directly the intrinsic viscosity (S/sub i/) using a VSM. The measurement is carried out in a number of measurement steps. In each step, the applied field (H/sub a/) behavior with time is gradually adjusted according to the change in H/sub 1/ calculated from the relaxation behavior measured from the previous measurement step. Eventually, during the last step, H/sub 1/ is kept constant by appropriately changing H/sub a/. The ultimate viscosity obtained from the last step is the intrinsic viscosity at this constant H/sub 1/. Automatic measurements were carried out on two samples: a sputtered CoCrPtB perpendicular media and a Co-filled alumite media. Commonly, the ultimate S/sub 1/ for these types of samples can be obtained after 4 to 6 steps Throughout the steps the deviation of H/sub 1/ (from that at the start of the relaxation) goes asymptotically to zero and the viscosity increases and saturates at the ultimate value. The viscosity obtained using our method is believed to reflect better the real intrinsic viscosity of perpendicular media Moreover, we proposed a model that allows to simulate the measurements. The simulation fits quite well with our observations. With the model, we can understand and predict the behaviors of samples during the measurements. Using this model, we proposed away to make a "shortcut" in the real measurements. By using this "shortcut", even with high susceptibility samples, the ultimate viscosity value can still be obtained after a few steps.