Electron energy loss spectroscopy of rare earth-transition metal compounds and their hydrides ReMn2(H2) (Re=Gd,Er) aided with ab initio calculations using WIEN2k

Full text: Electron Energy-Loss Spectroscopy (EELS) in a transmission electron microscope EELS is a versatile tool for the study of solids and is under constant development. Especially EELS in the low-loss region up to 50 eV is under a scope nowadays. The rare earth-transition metal compounds easily absorb hydrogen, which is causing many changes in their physical properties, in particularly structural and magnetic ones. Hydrogen introduced into the bulk influences the electronic structure of the material. The ErMn2 and GdMn2 and their hydrides are interesting for basic and applied research. Specimens were prepared from series of powders of pure GdMn2, ErMn2 and hydrogenated GdMn2H2, ErMn2H2 compounds. Powders were embedded in epoxy-resin and cut with an ultramicrotome. Despite the brittleness of the material a number of sufficiently thin cuts of grains with an average thickness of about 100 nm were obtained. A series of valence EELS (VEELS) spectra up to 50 eV were acquired. Differences in pure and hydrogenated samples were found. The main peak of the VEELS spectrum is shifted, for hydrogenated specimens it is about 2 eV higher for both compounds. The interpretation of this effect and other features in the VEELS spectrum in investigated materials is aided by ab initio calculations using the WIEN2k code. We found that the number of free electrons per volume unit increased for hydrogenated samples as it was expected. (author)