Determination of basic magnetic unit size in CoCrTa/Cr magnetic disk media

The magnetic transition region in a CoCrTa/Cr hard disk has been studied with high-resolution Foucault-mode Lorentz microscopy. It was found that the amplitude of the zigzag transition increases significantly at the track edges. Imaging results show that the CoCrTa grains behave magnetically in a clustered manner, forming domains of varying sizes at the transition. The dimension of the smallest grain cluster [or the basic magnetic unit (bmu)] has been determined by studying a pair of antiparallel domain contrast images in this medium, Investigations also reveal that each bmu consists of six to eight CoCrTa hcp grains, giving an average bmu unit size of about 80±12 mm. Furthermore, the magnetic domain images indicate that the mechanical texture induced by polishing does not break up this intergranular coupling