High-resolution MFM: Simulation of tip sharpening

Abstract

Abstract-The transfer functions of tips with various sharpened tip ends were calculated and the resolution of these tips was estimated by considering the resolution limit due to thermal noise at room temperature. The tip having an ellipsoidal tip end (ellipsoidal tip) is found to be a suitable candidate for high-resolution magnetic force microscopy. Sharpening of the flat tip end makes zero signal frequencies disappear for tips with ellipticities larger than tan 45 . The sensitivity shows a maximum around an ellipticity of tan 80 . The ellipsoidal tip shows a much smaller tip thickness dependence compared to the tip having a flat tip end because only the tip end mainly contributes to signals in case of the ellipsoidal tip.

Simulation of high-resolution MFM tips for high-density magnetic recording media with low bit aspect ratio

“…The sensitivity shows a maximum in the range of ellipticity around tan 701. The phenomena are similar to those for the one-dimensional media with infinite BAR [5]. The zero signal character arises from the same origin as those of gap zeros in magnetic recording heads.…”

“…The sharpened bar tips having two ellipsoidal flat planes at the tip-end were found to have high-resolution in the range of high ellipticity. On increasing the ellipticity of ellipsoidal tip-end planes, zero signal spatial frequencies disappear in the range of ellipticity larger than tan 451 and the sensitivity of tips has a maximum around tan 801 [5]. However, with decreasing BAR of media, the resolution of ellipsoidal tips is predicted to decrease due to the occurrence of zero signal frequencies in the cross track direction.…”

“…The magnetization of the tips is perpendicular to the surface (M z ¼ M t ), which means there is no fluctuation of magnetization direction during the observation. The MFM signal is expressed by the following equation [5][6][7]:…”

Simulation of high-resolution MFM tip using exchange-spring magnet

“…Each hard magnetic layer has the same thickness and magnetization of the tip, and the sample is considered to have no fluctuation. The MFM signal for a sample with a periodic magnetic surface charge density is calculated using the following equation [6,7]:…”

“…From calculations with changing k x , the MFM transfer function is then obtained using the following values (identical to those in Refs. [6,7]): S ¼ 100 nm, Dl ¼ 1 mm, M(Sample) ¼ 295 kA/ m, t ¼ 70 nm and tip-sample distance z 0 is 10 nm.…”