Analysis of Mössbauer Hyperfine Structure in Thulium Metal below the Néel Temperature

Mössbauer-effect measurements of the hyperfine structure of ${\mathrm{Tm}}^{169}$ below the Néel temperature are presented and analyzed. The interpretation is based on the neutron diffraction analysis of the magnetic structure, and assumes fast relaxation among the exchange-split levels of the lowest $J$ multiplet. The assumption of slightly incommensurate magnetic and crystal unit cells is essential to the successful interpretation of the data, since it produces a continuous distribution of hyperfine fields, as is observed.