Transverse susceptibility of hard-disk media by dc methods

A torque method for measuring the transverse susceptibility of magnetic recording media is discussed. With respect to the previous methods involving an ac probe field H-P, the present method introduces a concept of measurement involving a dc H-P. The high precision of the proposed method makes it suitable for modern hard-disk media, unlike the previously reported methods. The measurement of the transverse susceptibility is performed in two different experimental conditions, denoted by zero-field blocked and field blocked, allowing a straightforward interpretation of the thermal relaxation effects on the transverse susceptibility. A theoretical interpretation of the experimental results is also proposed, that is based on the Stoner-Wohlfarth and two-level models. The proposed theory could be used for extracting the anisotropy field distribution from the experimental dc transverse susceptibility. (C) 2003 American Institute of Physics.