Optimization of lateral resolution in magnetic force microscopy

Abstract

Magnetic force microscopy (MFM) plays an important role in magnetic recording research. It is not only suited for the study of magnetic heads and recording media, but is also a possible technique for ultrahigh-density bit writing. One of the key properties of this technique is the geometric simplicity of the magnetic field-detecting element-which makes it suitable for reaching very high lateral resolution.

High-resolution MFM: Simulation of tip sharpening

“…The tip having an ellipsoidal tip end is found to be a better candidate for high-resolution MFM, than the flat tip end suggested in [5]. The sharpening of the flat tip end makes zero signal frequencies disappear for tips with ellipticities larger than and the sensitivity shows a maximum around an ellipticity of .…”

“…The resolution can be estimated by the intersecting point between a certain transfer function and the noise level. This point represents the critical wavelength [5]. As seen in Fig.…”

“…Here, no fluctuation of the tip and sample magnetization is considered. The MFM signal for a sample with a periodic 0018-9464/03$17.00 © 2003 IEEE magnetic surface charge density is calculated by using the following [5], [6]: (1) The calculations were carried out for tips with three different tip-end shapes: flat, triangular, and ellipsoidal. From calculations with changing , the MFM transfer function is then obtained using the following values (identical to those in [7]):…”

Magnetic Force Microscopy — Towards Higher Resolution

“…The only thing left unknown is the magnetisation distribution in the MFM tip, which can be very complex. We will restrict ourselves however to the bar type tip with a magnetisation fixed along the z-axis (Figure 4), in the first place because this is the ideal MFM tip shape [21] and in the second place because it results in very illustrative closed-form equations. The procedure to obtain the force F z involves a simple integral of the stray field over the recangular tip volume, and taking ∂U/∂z [21]:…”

“…In STM and AFM only the last atom determines the signal, but in MFM a much larger part of the tip takes part in the image formation. Therefore the optimum tip shape is not a sharp needle but a bar or cylinder with a flat front end [21], analogue to a hard disk head for perpendicular magnetic recording. The fact that the bar shape is the optimum shape for MFM can perhaps be most easily understood by considering the magnetic charge distribution in a tip with an ideal uniform magnetisation (see figure 15).…”