Magnetic Imaging in the Presence of an External Field: Erasure Process of Thin Film Recording Medium - Magnetics, IEEE Transactions on

imaged by applying a progressively increasing external magnetic field. Images from magnetic force microscopy with an in situ magnetic field revealed features attributable to probe-induced and sampleinduced effects. The probe effects result in the preferential sensitivity of the MFM imaging to the component of the local sample field in the direction of the probe's magnetization. The reorientation of the probe's magnetization with respect to the Sample plane direction causes the change in instrument response from detecting surface magnetic charges (magnetization divergence sensing) to detecting the surface magnetization distribution. Sample effects are more prominent at higher fields and the micromagnetic features of the recorded patterns follow a characteristic sequence as the unfavorably magnetized areas switch in the direction of the external f i e l d . was oriented primarily along the surface plane and in the direction of the recorded tracks. The average strength of the external field was calibrated against the input current by using a miniature Hall probe and achieved as high as 3000 Oe with tolerable Joule heating. Imaging drifts due to thermal effects were insignificant and fluctuations in the applied field were minimal. Space limitations of this paper preclude detailed discussion of the design which will be furnished elsewhere. The sample was prepared from a conventional removable rigid disk whose characteristics have previously been studied [ 11. Standard magnetization curves were measured using a vibrating sample magnetometer and the following macroscopic properties were obtained: H, = 926 Oe, Mr6 = 5.0 memu/cm2, S=0.81, S*=0.86, and the in-plane orientation ratio M,@ar)/Mr(per)-l.5 and positive particle interaction. The data consists of more than 100 images taken in succession, each of which is associated with a fixed external field and taken in increments of about 10 Oe near the medium coercivity.