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Measurement of the stray field emanating from magnetic force microscope tips by Hall effect microsensors

We describe the use of micronic Hall sensors as magnetic-field profilometers with submicron resolution. The procedure involves the deconvolution of Hall voltage maps produced by scanning the field source over the sensor, with a scanning probe microscope. The response function of an infinite Hall cross is calculated analytically in the two-dimensional case, using conformal mapping techniques. Various methods of deconvolution of the Hall voltage maps are presented and compared. The calculated response function is used for the deconvolutions, and different effective sensor sizes are tried. It is shown that the remaining main uncertainties come from the ignorance of the true response function of the sensor, ascribed to the charge depletion phenomenon that is known to occur at the sensor edges. The method is applied to thin-film magnetic force microscope tips for which a precise knowledge of the tips field at sample location proves crucial to image interpretation. Maximum fields in the range 10–100 Oe are found at a distance known to be about 100 nm from the tip contact surface, depending on the tip coating thickness and magnetization direction.