Studying Magnetism with X-Ray Standing Waves

A new method for studying the magnetic structures at the atomic level was developed within the scope of this thesis. A combination of the site-selectivity of the diffraction-based x-ray standing waves (XSW) technique and sensitivity to magnetic properties of the x-ray magnetic circular dichroism (XMCD) spectroscopy leads to a completely new perspective. The XSW method makes use of the standing wave appearing as a result of an interference between the incoming and the Bragg reflected electromagnetic waves. In the magnetic x-ray standing waves (MXSW) technique, a circular polarisation of the incoming beam is used to additionally gain magnetic information via the dichroism in the absorption of the standing wave. Due to the utilisation of the x-ray interference field, the phase information is preserved, so the magnetic structure can be studied directly. The shape of the modulation in the MXSW signal is characteristic of a given distribution of the magnetic moments and yields directly structural information. The development of the new method within the scope of this thesis consisted firstly of constructing the theoretical foundations. The dynamical theory of x-ray diffraction is used to treat theoretically the scattering phenomena. The absorption of the resulting wavefield is described within the framework of the time-dependent perturbation theory. Secondly, the simulations for several systems with different magnetic ordering were conducted. The simulation results were later used to explain the observed experimental data. Finally, two MXSW experiments were performed on a platinum-cobalt alloy and an yttrium-iron-garnet single crystals. The resulting angle-dependent XMCD signals exhibit a clear variation caused by the x-ray standing wave. The comparison between the simulation results and experimental data confirmed the validity of the novel MXSW theory