For the development of increased density of data storage in magnetic recording, it is very important to produce highly efficient magnetic heads with an optimized head design for the read/write purposes. To prove design parameters, it is necessary to exactly evaluate the magnetic stray-fields and to detect possible flux leaks in model heads. Our model heads are a Ferrite read head and a MIG (metal-in-gap) write head. The investigations are carried out in electron microscopes, which are equipped with a special lens for magnetic field-free imaging. Qualitative examinations of the stray-field were carried out in Foucault technique on a Philips CM30. A quantitative measurement could be achieved usind the DPC-technique [1] (differential phase contrast) in a JEOL 2000 FX with a special 4-quadrant-detector. From the collected DPC data sets a 3D reconstruction of the stray-field, based on the Algebraic Reconstruction Technique [2] or the Radon Tranform Method [3] was possible. In parallel, for the MIG-heads TEM observations of the interface region between the Ferrite material and the metal coating were carried out. From these investigations the following results could be gained: (1) From linescans (taken at about 0.5 μm from the poletip surface, see fig. 1) it is obvious that the stray-field of the MIG head is more localized and shows a higher overall maximum compared to the Ferrite head. A tomographic field reconstruction has been performed to obtain the 3D character of the stray-field of the Ferrite-head at about 0.25-0.375 μm from the poletip surface. From this reconstruction, the extent and strength of the 3D stray-field can be seen directly. (2) From a "BH"-loop, acquired at the center of the polegap of the MIG-head it can be seen (fig.2), that up to approximately 25 mA of driving current a steady increase of the strength of the stray-field is achievable. For currents higher than 25 mA, the strength of the stray-field remains constant. For the MIG head additional stray-fields (secondary gaps) at the Ferrite-softmagnetic interface can clearly be observed. (3) From TEM investigations of the Ferrite/metal interface region in MIG-heads, an insufficient match between the structures was found, which leads to a weak magnetic coupling and generates the observed "secondary gaps". This explains the unsatisfactory electrical response properties. The magnetic and structural matching can be improved by using a thin functional film between the two materials.
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