Calculation of playback signals from MFM images using transfer functions

Magnetic force microscopy has proven to be a suitable tool for analysis of high-density magnetic recording materials. Comparison of the MFM image of a written signal with the actual read-back signal of the recording system ca n give valuable insight in the recording properties of both heads and media . In a first order approach one can calculate a 'signal' by plotting the li ne integral over the track width along the track direction (Glijer et al., IEEE Trans. Magn. 32 (1996) 3557). The method however does not take into ac count, the spatial frequency dependence of the transfer functions of both t he MFM and the readback system. For instance the gap width of the head (lim iting the high frequency signals) and the finite length of the MFM tip (lim iting the sensitivity for low frequencies) are completely disregarded (Port hun et al., J. Magn. Magn. Mater. 182 (1998) 238). This type of problem inv olving spatial frequencies can be very elegantly solved in the Fourier spac e. The response of the MFM is described by the force transfer function (FTF ) as introduced by (Porthun et al. (J. Magn. Magn. Mater. 182 (1998) 238) a nd Hug et al. (J. Appl. Phys. 83 (1998) 5609), which describes the relation between the MFM signal and the sample stray field at the height of the tip . From this stray field an 'effective surface charge distribution' can be c alculated, by means of the field transfer function (HTF). The same function HTF can be used to calculate the stray field at the height of the head. Fr om this stray field the playback voltage can be calculated, resulting in th e playback transfer function (PTF). In order to do this the Karlquist model had to be extended to three dimensions. (C) 1999 Elsevier Science B.V. All rights reserved.