Multi-frequency Fluxgate MFM

In the recent years, progress in atomic force microscopy (AFM) led to the multi-frequency imaging paradigm in which the cantilever-tip ensemble is simultaneously excited by several driving forces of different frequencies. By using multi-frequency excitation, various interaction forces of different physical origins such as electronic interactions or chemical interactions can be simultaneously mapped with topography. However, a multi-=frequency magnetic imaging technique has not been demonstrated.

In this project, we consider a multi-frequency magnetic imaging method which uses first resonant flexural mode for topography signal acquisition and second resonant flexural mode for measuring the magnetic interaction simultaneously. As in a fluxgate magnetometer, modulation of magnetic moment of nickel particles attached on the apex of an AFM tip can be used to modulate the magnetic forces which are dependent on external DC fields through the nonlinear magnetic response of the particles. Coupling strength can be varied by changing coil current or set point parameters of the MFM system. Special MFM tips were fabricated by FIB and magnetically characterized for the purpose of multi-frequency imaging. In this work, the use of such a nano-flux-gate system for simultaneous topographic and magnetic imaging is experimentally demonstrated. The excitation and detection scheme can be also used for high sensitivity cantilever magnetometry.

O. Aktaş, A. Dana, M. Bayindir