TABLE OF CONTENTS Within recent years spin-polarized scanning tunneling spectroscopy (SP-STS) has developed into a mature tool for ultrahigh spatial resolution magnetic domain imaging. In this chapter, we will introduce the measurement principle of SP-STS and describe experimental procedures and requirements. We will discuss present data measured on different ferro- and antiferromagnetic sample systems demonstrating the particular strength of SP-STS, i.e., the ability for simultaneous observation of structural, electronic, and magnetic properties.
As already described in the previous chapter, spin-polarized electron tunneling in planar tunnel junctions has been a well established experimental technique since the early 1970s [1] , [2]. The power of persuasion of these first experiments was based on an appropriate choice of electrode materials, i.e., a ferromagnetic and superconducting electrode, in combination with the use of spectroscopic techniques.
The planar tunnel junctions were fabricated by growing a thin ferromagnetic film on an oxidized, self-passivating aluminum sample. The thin layer of aluminum oxide served as a tunneling barrier. In particular, the electronic properties of the superconductor (aluminum at T = 0.3 K) played an important role. Close to the Fermi level its quasiparticle density of states (DOS) is dominated by two peaks separated by a small gap with a width of a few meV. If exposed to a strong external field, the Zeeman energy leads to an additional well-defined spin splitting of both peaks leading to four peaks, two of which exhibit a polarization parallel to the magnetization of the ferromagnet and...
