YMn2Hx and RMn2-yFeyH6 (R = Y, Er) studied by Raman, infrared and inelastic neutron scattering spectroscopies

YMn2 forms either interstitial YMn2Hx hydrides for x <= 4.5 or a complex YMn2H6 hydride when submitted to high hydrogen pressure. These compounds have been studied by inelastic neutron scattering (INS) in order to clarify the different modes of H vibration. The INS spectra of YMn2Hx hydrides are strongly dependent on the H content. YMn2H6 and YMn2D6 show broad bands, also observed by Raman and IR spectroscopy, assigned to H-Mn-H (or D) and Mn-H bending and stretching modes. Both ErMn2D6 and ErMn1.8Fe0.2D6 show, in addition to the H vibration mode, an intense band at 215 cm(-1) which has been attributed to a magnetic excitation of Er3+ in view of its momentum transfer dependence.