Detection of nonmagnetic metal thin film using magnetic force microscopy

Magnetic force microscopy (MFM) allows detection of stray magnetic fields around magnetic materials and the two-dimensional visualization of these fields. This paper presents a theoretical analysis of the oscillations of an MFM tip above a thin film of nonmagnetic metal. The results show good agreement with experimental data obtained by varying the tip height. The phenomenon analyzed here can be applied as a "metal detector" at the nanometer scale and for contactless measurement of sheet resistivity. The detection sensitivity is obtained as a function of oscillation frequency, thus allowing determination of the best frequency for phase-shift measurement. The shift in resonance frequency due to the presence of a nonmagnetic metal is also discussed.