Observations of single magnetic domain wall in nanomagnet by magnetic force microscopy

Magnetic force microscopy (MFM) with a low moment probe and Q-control in a vacuum was applied to a permalloy semicircular wire loop with a single magnetic domain wall (DW). We successfully observed a nearly free single DW in such a nanomagnet, which is easy to move even using weak magnetic fields. In the case of MFM measurement with a high moment probe, the effects of the probe's stray field caused "DW manipulation," and the MFM signal was maximized just above the wire. When using the low moment probe, the MFM signal was maximized at the side of the wire, which concurs with the result of micromagnetic simulation.