Structural and magnetic transformations in HoMn2Hx hydrides

The HoMn2 compound crystallizes in the C15 or C14 Laves phases depending on preparation. The effect of hydrogen absorption on structural, magnetic and thermodynamic properties of HoMn2Hx hydrides for both phases has been investigated by XRD, AC/DC magnetometry, and calorimetry in the temperature range of 80-300 K. In addition to general features revealed by RMn2Hx compounds (R= rare earth or Yttrium), unusual behavior of these hydrides was found. In particular, a transformation from the cubic to the monoclinic structure was detected, which so far has not been reported for other cubic RMn2Hx (R - rare earth or Yttrium) compounds. The structural transformations are reflected in the magnetic behavior. The change in ordering temperatures indicates a strong correlation between the magnetic interactions and the Mn-Mn distance modified by hydrogen absorption. Tentative magnetic and structural phase diagrams are proposed. The presented results are compared with the properties of other cubic and hexagonal RMn2Hx hydrides.