Imaging Magnetic Microspectroscopy

There are several well established techniques for spectroscopy of magnetic films and surfaces that are commonly employed when information about electronic states, binding properties, or element-resolved magnetic properties is required. The reduction in lateral size that goes along with the soaring extent to which magnetic elements and devices are used or planned to be used in technological applications in magnetic sensors, data storage, or magneto-electronics demands magnetic spectroscopic information on a microscopic lateral length scale. Thus, the combination of magnetic spectroscopy and microscopy into what is commonly termed microspectroscopy or spectromicroscopy would be ideal for the study of small magnetic structures.

This chapter explains the combination of photoelectron emission microscopy (PEEM) and X-ray magnetic circular dichroism (XMCD) in absorption for imaging XMCD-PEEM microspectroscopy. In a PEEM, an electrostatic electron optics creates a magnified image of the secondary electron intensity distribution at the sample surface. When excited by soft X-rays, the image intensity can thus be regarded as a local electron yield probe of X-ray absorption. In XMCD, the measurement of the total electron yield of the sample is frequently used to determine the X-ray absorption as a function of photon energy and helicity of the circularly polarized radiation. Consequently, scanning the photon energy and recording PEEM images at each photon energy step for both helicities results in a microspectroscopic data set that allows one to extract the full information that is usually obtained from XMCD spectra for each single pixel of the images. Of particular interest is therefore the application of the so-called sum rules to extract the effective spin moment and the orbital moment, projected onto the direction of incoming light. This chapter starts with a short overview of magnetic microspectroscopy techniques in comparison to XMCD-PEEM microspectroscopy. The basics of the underlying spectroscopic and microscopic methods are briefly explained in Sect. 1.2. Important experimental aspects inherent to XMCD-PEEM microspectroscopy are discussed in Sect. 1.3. Finally, in Sect. 1.4, two recent examples of application of XMCD-PEEM microspectroscopy are presented, in which the method has proven beneficial for the study of interesting issues in the field of ultrathin magnetic films.