Magnetization reversal and coercivity of magnetic-force microscopy tips

Abstract

An experimental technique is presented that allows determining the magnetization reversal and coercivity of magnetic-force microscopy (MFM) tips. An Ω-shaped current carrying gold ring with a radius of 2400 nm fabricated by electron-beam lithography and a lift-off technique is charged with a constant current in order to produce a magnetic stray field in the z direction that is detected by MFM. While an oscillating MFM tip is continuously raster scanned across the center of the current ring, an external magnetic field is applied in the z direction and increased in magnitude in order to reverse the tip magnetization during imaging. Thus, the corresponding changes in the measured image contrast exclusively describe the magnetization reversal and coercivity of the particular part of the tip that is used for imaging. We have investigated commercially available thin-film tips and we find that the hysteresis loops measured with MFM may be significantly different as compared to hysteresis loops measured by means of superconducting quantum interference magnetometry on the respective magnetic tip coatings of the same tip.

Micromagnetic studies of cobalt microbars fabricated by nanoimprint lithography and electrodeposition

“…This field is too low to induce the change of magnetization configuration in the sample. However, since the CoCr MFM tip coating is magnetically harder than studied microbars (coercivity $360 Oe [41,42]), and the field at the tip surface determined by electron holography is 620 Oe [43], which is higher than the saturation magnetization of microbars in the plane, it is possible that the micromagnetic configurations were affected by the MFM tip while performing intermittent contact mode scans. Magnetic field of the tip, perpendicular to the sample surface, could initiate vortex formation.…”

“…Lift height was 100 nm. tips [41], calculated tip field was $16 Oe. This field is too low to induce the change of magnetization configuration in the sample.…”

Quantitative analysis of magnetization reversal in submicron S-patterned structures with narrow constrictions by magnetic force microscopy

“…[7][8][9][10][11] To quantitatively obtain the magnetic moment of the sample, some studies are focused on the method to determine magnetic reversals of MFM tip. 12,13 However, for the simpler case, when the sample with switching field is much less than that for the MFM tip, the MFM phase-shift should be basically quantifiable. In this letter, we provide quantitative MFM analysis for multidomain submicron wire, which also correlates with the magnetoresistance ͑MR͒ measurement and simulation.…”

Numerical computation of magnetic fields applied to magnetic force microscopy

“…This tip consists of a cobalt-chromium compound, which is orthogonally magnetized with respect to the sample surface. Analogous to (Carl et al, 2001), we set the value for the magnetization in negative y-direction to M ¼ 749 kA/m. Furthermore, we assume such a hard ferromagnetic material, so that the permanent permeability of the pyramidal tip is approximately m r < 1.…”