Magnetic study of the Ce2Fe17Hx compounds: Magnetic circular x-ray dichroism, x-ray-absorption near-edge structure, magnetization, and diffraction results

Abstract

Hydrogen insertion in the ${\mathrm{Ce}}_2$ ${\mathrm{Fe}}_{17}$ ${\mathrm{H}}_{\mathit{x}}$ system leads to spectacular changes of the physical properties. A relative increase of the Curie temperature of almost 100% is observed as well as the highest volume increase. In addition to previous neutron diffraction measurements which pointed out an increase of the local iron moments, we present in this paper absorption and magnetic circular x-ray dichroism (MCXD) experiments performed at the ${\mathit{L}}_{2,3}$ edges of Ce and the K edge of iron. These measurements allow us to study the evolution of the Ce electronic structure upon hydrogen insertion. Values for the Ce valence have been derived from both absorption and MCXD signals. The MCXD data are analyzed for their shape, intensity, and sign, and compared to the macroscopic magnetic measurements. It is shown that in these compounds the Ce atoms bear a 5d magnetic moment, which is coupled antiferromagnetically to that on iron. There is no orbital contribution to this 5d moment which is thus solely of spin origin. The values of the 5d moment are deduced as a function of each composition in the ${\mathrm{Ce}}_2$ ${\mathrm{Fe}}_{17}$ ${\mathrm{H}}_{\mathit{x}}$ system at low and room temperature. At the K edge of iron, the shape and intensity of the dichroic signal have been related to the filling of the majority 3d band.