Linear dichroism Natural or Magnetic (XLD, XMLD)
Variations in the crystal structure of the materials makes the absorption of X-rays different depending on the orientation of the electric field of the beam and the crystal axes of the specimen. This effect is known as X-ray Linear Dichroism (XLD) and is a powerful source of information on changes in the structure of interfaces and surfaces of thin films and multilayers. In addition, the absorption of linearly polarized radiation may vary with the magnetization of the sample. In this case, we are dealing with Linear X-ray Magnetic Dichroism (XLMD) and we have magnetic information with chemical sensitivity.
Magnetic Circular Dichroism (XMCD)
Materials which have a nonzero magnetic moment absorb differently in the two possible helicities of circularly polarized X-rays (left and right circular polarization). This difference is called circular dichroism, and when applied to the absorption edge of the components of the sample, it allows for the magnetic contribution of each chemical element independently. Furthermore, in many cases it is possible to determine the spin and orbital components of the magnetism. The dichroism signal is overall maximum in the peak of the absorption edge of each element. Keeping the fixed energy at this point of the spectrum and varying the applied magnetic field, it is possible to obtain curves of magnetic hysteresis for each element in the composition of the sample. This is particularly important in the characterization of new permanent magnets.
Photoemission Spectroscopy with Angular Resolution (ARPES)
The electron analyzer that equips the SABIÁ beamline does not only determine the kinetic energy of the photoelectrons, but also its escape angle from the sample. Armed with this angle and kinetic energy, it is possible to determine the momentum of the emitted photoelectron. Applying the principle of conservation of momentum, it is possible to then infer the momentum of the electron in the crystal (before being emmited) and thus build the energy dispersion curve as a function of the angular momentum. This is one of the most important information about the electronic structure materials.
Photoelectron Emission Microscopy
Upon interaction with the X-ray beam, the materials emit electrons. This effect is particularly important in the region of soft X-rays. Using column similar to an electronic transmission microscope, it is possible to obtain images based on the electrons emitted in the absorption process. This is the basic principle of PEEM (photoelectron emission microscopy), which allows obtaining spectroscopic information with a spatial resolution of up to a few tens of nanometers. Furthermore, the XMCD and XMLD methods are still valid and by the proper use of the polarization of the X-ray beam, magnetic information can be obtained with such a spatial resolution. This possibility is particularly interesting in the study of domain walls and its dynamics. Moreover, given the inherent chemical sensitivity to absorption of X-rays, the technique is of great potential to geosciences, environmental studies, among others, where it is important to locate the spatial concentrations of various chemical elements in the sample.