Hydrogen induced changes in the crystal structure and magnetic properties of UCoGe

Hydrogen pressure of 0.5-140 bar has been applied to synthesize hydrides of UCoGe. Besides an α hydride crystallizing in the structure type of the parent compound, which loses the weak ferromagnetism found in pure UCoGe, two distinctly different β hydrides were identified. The almost pure β hydride (UCoGeH1.7) is a ferromagnet below TC = 50 K. The highest H2 pressures (>130 bar) produce admixture of another hydride called β′ hydride, with less H/f.u. and TC = 8 K, obtained presumably as a decay product of a full hydride UCoGeH2.0 unstable at ambient conditions. The value of the Sommerfeld coefficient of electronic specific heat γ increases over 100 mJ mol-1 K-2 for the magnetic hydrides. (paper)