Scanning Electron Microscopy with Polarization Analysis (sempa) and Its Applications

Scanning Electron Microscopy with Polarization Analysis (SEMPA) is a technique for directly imaging the magnetic microstructure of surfaces and thin films. SEMPA relies on the fact that secondary electrons emitted from a magnetic sample in a Scanning Electron Microscope (SEM) have a spin polarization which reflects the net spin density in the material. This spin density, in turn, is directly related to the magnetization of the material. By measuring the secondary electron spin polarization, SEMPA can be used for direct, high resolution imaging of the direction and relative magnitude of a sample's magnetization, in the same way that a SEM can be used to image topography by measuring the secondary electron intensity. The SEMPA technique has evolved from measurements over the past few decades in which various conventional electron spectroscopies were combined with electron spin sensitivity to investigate the magnetic properties of surfaces and thin films. Several reviews of this early work are available [1, 2, 3, 4]. SEMPA microscopes, also sometimes referred to as spin-polarized electron microscopes (spin-SEMs), made their initial appearance in the mid 1980s [5, 6, 7]. Several reviews of the SEMPA technique and instrumentation have appeared since then [8, 9, 10, 11]. SEMPA is one of several methods used for imaging magnetic microstructure. Since each method has its own particular strengths and drawbacks, the sample and type of imaging required determine which of these techniques is most useful. The basic