Texture induced variations in switching fields of hard disk media investigated by magnetic force microscopy

A method for mapping the microscopic spatial variation of switching fields in magnetic recording media using a magnetic force microscope is described. The sample magnetization is reversed by small field increments using an electromagnet. Differences between consecutive pairs of magnetic force images for the various remanent states show grains switching at different applied fields. A submicron-scale switching field map is derived from the difference images as well as images of cumulative magnetization change showing the progression of the magnetization reversal. Switching field distributions are constructed from the maps.; The method is applied to samples with different substrate textures to examine the effect of texture on magnetic switching behavior. Reversals are found to occur in chains along the applied field direction for fields coincident with the texturing and for untextured samples. This behavior is attributed to magnetostatic intergranular interactions. For fields applied transverse to the texture, no long range order is seen in the reversal process. In several of the samples the reversal process is confined by the texture grooves. The observed behavior supports a model in which the interactions between grains of the medium are disrupted by the texture leading to bulk magnetic anisotropies.