169Tm Mössbauer experiments in the paramagnetic phase of Tm2 Al

Magnetic and Mössbauer measurements have been made on the intermetallic compound Tm₂ Al from 1.4 to 300 K. The susceptibility data show Curie—Weiss behaviour with an effective magnetic moment of 7.7(1) μ_B per atom, cf. the free ion value of 7.56 μ_B. No evidence of magnetic ordering is found down to 1.4 K. By way of contrast, however, the¹⁶⁹Tm Mössbauer data at 1.4 K reveal two fully split six-line spectra, with differing magnetic and quadrupole hyperfine parameters. By 4.2 K, the weaker of the two sub-spectrum has collapsed to form a peak in the centre of the Mössbauer spectrum. At higher temperatures the intensity of the split sub-spectrum slowly disappears, while retaining a virtually temperature-independent magnetic splitting. Both the Tm sites in Tm₂Al therefore exhibit typical para-magnetic relaxation behaviour, with little or no cross-talk between the two Tm species. As with both TmAl and Tm₃Al₂, Tm₂Al exhibits unusually long relaxation times for a metallic material.