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MFM image of air-bearing surface of an HDD write-head. The MFM is sensing stiffness, due primarily to the vertical field component acting on the conical tip. Darker colors are lower stiffness (phase-lead) and lighter colors are higher stiffness (phase-lag). The difference in stiffness over the soft magnetic material versus non-magnetic material gives a means of calibrating the behavior of the tip and quantifying the magnitude of the fields observed. From the paper, "Fields From a Magnetized Conical Shell and Quantitative Magnetic Force Microscopy," by R. Wood and N. Smith, Art. no. 6500609.
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