Iterative method for intrinsic viscosity measurements on perpendicular recording media

We introduce a new method that allows one to directly measure the intrinsic viscosity (S_i) for perpendicular media using a vibrating sample magnetometer. The measurement is carried out in a number of iterations. In each iteration, the behavior of applied field (H_a) with time is gradually adjusted according to the change in the internal field (H_i) calculated from the relaxation behavior measured in the previous iteration. Eventually, during the last iteration, from which the intrinsic viscosity can be extracted, H_i is kept constant by appropriately changing H_a.