Crystal fields and exchange interactions in Yb2Fe17: A 174Yb Mössbauer study (abstract)

Abstract

Most rare-earth -(R) iron compounds R2Fe17 crystallize in the hexagonal Th2Ni17 structure with two inequivalent rare-earth sites in the unit cell. For Tm2Fe17 magnetic anisotropy of opposite character has been determined for the two Tm sites.1 Nevertheless, the axial anisotropy of one Tm site dominates at low temperatures and forces the magnetic moments to the direction parallel to the c axis below the spin-reorientation temperature TSR=74 K. Magnetization measurements on Yb2Fe17 gave no indication for a spin reorientation.2 In this compound, the Fe sublattice anisotropy seems to dominate at all temperatures, confining the moments to the plane perpendicular to the c axis. This has now been confirmed by 174Yb Mössbauer spectra of Yb2Fe17 in the temperature range 1.6–100 K. The different crystal fields acting on the Yb 4f shell at the two sites lead to a large difference in the static moments as revealed by the different hyperfine fields. From the temperature dependence of the magnetic and electric hyperfine interactions, values for the crystal-field parameters and exchange fields at both Yb sites have been derived. Structural disorder, probably due to random occupation of Yb sites by Fe2 dumbbells, leads to distributions of the crystal-field parameters and to considerable broadening of the Mössbauer spectra.