The knowledge on the domain structure of ferro- as well as antiferromagnetic surfaces is essential for the understanding of many physical effects as, e.g., the exchange-bias effect and exchange-coupling in magnetic multilayers. However, especially the investigation of antiferromagnets is difficult because of the lack of a macroscopic magnetization. Spin-polarized scanning tunneling microscopy/spectroscopy (SP-STM/STS) using magnetic probe tips has long been considered as a promising tool in order to study magnetic properties down to the atomic scale.