Differential Magnetic Force Microscopy with a Switchable Tip

TL;DR

This paper introduces a novel magnetic force microscopy technique that uses a switchable tip to distinguish magnetic forces from other interactions in a single scan, enhancing measurement accuracy and sensitivity.

Contribution

The authors developed an inverted MFM setup with a periodically flipped magnetic tip, enabling force separation without multiple measurements, and proposed future improvements for higher sensitivity.

Findings

Successful separation of magnetic and non-magnetic forces in a single scan

Potential for three orders of magnitude sensitivity improvement

Implementation of a miniaturized electromagnet for tip magnetization switching

Abstract

The separation of physical forces acting on the tip of a magnetic force microscope (MFM) is essential for correct magnetic imaging. Electrostatic forces can be modulated by varying the tip-sample potential and minimized to map the local Kelvin potential. However, distinguishing magnetic forces from van der Waals forces typically requires two measurements with opposite tip magnetizations under otherwise identical measurement conditions. Here, we present an inverted magnetic force microscope where the sample is mounted on a flat cantilever for force sensing, and the magnetic tip is attached to a miniaturized electromagnet that periodically flips the tip magnetization. This setup enables the extraction of magnetic tip-sample interactions from the sidebands occurring at the switching rate in the cantilever oscillation spectrum. Our method achieves the separation of magnetic signals from other force contributions in a single-scan mode. Future iterations of this setup may incorporate membrane, trampoline, or string resonators with ultra-high quality factors, potentially improving measurement sensitivity by up to three orders of magnitude compared to the state-of-the-art MFM systems using cantilevers.