169Tm Mössbauer effect and magnetic study of Tm6Mn23 and its ternary hydride

The magnetic properties and the lattice constants of Tm₆Mn₂₃ were determined before and after hydrogen absorption. The compound Tm₆Mn₂₃ is ferrimagnetic with an ordering temperature T_c = 404 K. After hydrogen absorption the magnetization is strongly reduced and does not point to the occurrence of magnetic ordering. The strongly increasing hyperfine splitting observed by means of ¹⁶⁹Tm Mössbauer spectroscopy in the hydride for temperature below 60 K, however, shows that the Tm sublattice becomes magnetically ordered after H₂ absorption as well. In uncharged and charged Tm₆Mn₂₃ the values of the Tm moments are close to the free ion values.