Micro-indentation and scanning probe microscopy to assess multilayer magnetic film damage

We have combined several techniques to evaluate the effect of mechanical de formation on the topography and magnetics of an underlying thin magnetic fi lm. Micro-indentation techniques are used to introduce tailored deformation s to magnetic recording disks. Atomic force microscopy (AFM) and magnetic f orce microscopy (MFM) then map out the topography of the indentations and t he effect on the underlying magnetic film. Indentation morphology includes pyramidal and conical indents, linear scratches, and reciprocating wear tra cks. The extent of topographical damage assessed by AFM correlates with the carefully controlled normal and tangential forces of the micro-indenter. S ub-surface 'damage' is assessed by MFM, monitoring for loss of resolution i n pre-written magnetic data tracks. Mechanical tests are conducted at very low speeds and loading rates; hence, frictional heating or other thermo-mec hanical factors that might cause ambiguities in data interpretation can be safely ruled out. By using the combination of micro-mechanical testing, Ram an spectroscopy, and AFM/MFM techniques, we have found that mechanically in troduced bit contrast degradation is attributed to physical modification of the magnetic coating and protective overlayer. The indentation and scratch tests both confirm that static pressure alone is not sufficient to cause t he observed magnetic degradation; other mechanical factors must be invoked, including alteration of the geometry of the magnetic coating. Microwear is capable of causing magnetic damage at much lower pressures than indentatio ns or scratches. From wear track data, the degree of disk surface damage is correlated with the degree of magnetic bit contrast degradation. From wear track data on DC-erased samples it is concluded that mechanical deformatio n can induce magnetic contrast via concerted reorientation of grain c-axis and, hence, reorientation of magnetic moments. (C) 2000 Elsevier Science B. V. All rights reserved.