STM-SQUID microscopy using a fine probe

Abstract

We developed an STM-SQUID microscope by combining a scanning tunneling microscope (STM) and a superconducting quantum interference device (SQUID) in order to observe the local magnetic structure of magnetic materials. The STM-SQUID microscope features a high permeability permalloy probe placed between the SQUID and the sample to serve as a flux guide. The magnetic field of the sample surface was effectively transmitted to the SQUID using this method, so it substantially improved the spatial resolution. However, simulation experiments showed that the shape of probe tip greatly influenced the spatial resolution of the magnetic field images, so we investigated this phenomenon further. The signal-noise ratio in magnetic images obtained with the STM-SQUID microscope is improved by using a permalloy probe for which the radius and cone angle of the probe tip are small.