We measured the high-resolution magnetic images using an STM-SQUID microscope that combines a high-Tc superconducting quantum interference device (SQUID) with a scanning tunneling microscope (STM). In the STM-SQUID microscope, the STM probe plays the important role of a flux guide and is responsible for tunneling current detection. Therefore, it is essential to investigate the probe itself in order to improve the magnetic image resolution. We optimized the electrochemical polishing condition to

more »

... realize the fine probe with a tip radius of 50 nm or less. We fabricated the various shaped probes by controlling the voltage during sharpening. The tip radius of 50 nm or less was achieved when the probe tip was sharpened at the applied voltage of 30 V. We then measured the magnetic images of typical magnetic materials, such as a steel sample and nickel thin films, using the probe with a tip radius of 50 nm or less. The magnetic domain structures were observed clearly.