Neutron diffraction and Mossbauer study of the magnetic structure of HoFe/sub 6/Sn/sub 6/

Abstract

We have used Time-of-Flight (ToF) neutron powder diffraction, and both 57 Fe and 119 Sn Mössbauer spectroscopy, to study the independent magnetic ordering behavior of the Fe and Ho sublattices in HoFe 6 Sn 6 . The crystal structure of HoFe 6 Sn 6 is orthorhombic (space group Immm). The Fe sublattice orders antiferromagnetically with a Néel temperature of 559(5) K, determined by differential scanning calorimetry. The ToF neutron diffraction patterns obtained at 30 K and 295 K show that the antiferromagnetic ordering of the Fe sublattice is along [100] with a propagation vector q = [010]. The magnetic space group of the Fe sublattice is and the Fe magnetic moment at 30 K is 2.31(5). This magnetic structure is confirmed by our 119 Sn Mössbauer spectra in which 37% of the Sn nuclei experience a substantial transferred hyperfine field from the Fe sublattice while the remaining 63% of the Sn sites show no magnetic splitting, due to the cancellation of transferred hyperfine fields from the Fe neighbors, in full agreement with our Wigner-Seitz cell calculations for each of the eight Sn sites in the HoFe 6 Sn 6 structure. The Ho sublattice orders ferromagnetically at 9(1) K. ToF data obtained at 4 K show that the Ho moments are aligned along [001] i.e., perpendicular to the Fe ordering. The magnetic space group of the Ho sublattice is . The refined Ho magnetic moments at 4 K are 4.4(2) and 5.2(2) at the 2a and 4h sites, respectively.

119Sn Mössbauer effect study of UxFe6Sn6 (x=0, 0.2, 0.4, 0.6)

“…The non-zero B transf on Sn(2e) arise from the ordered Fe moments as explained above. On the other hand, as in the case of Dy x Fe 6 Sn 6 (x < 0.5) [8] the highest B transf , similar to those reported for RFe 6 Sn 6 [3,5,7], was assigned to Sn(2e) with uranium NN and the lowest B transf , similar to that reported for Sn(1a) in FeSn, to Sn(2e) with neither uranium NN nor uranium next-nearest neighbours, NNN, i.e., in domains with a structure very similar to the FeSn one. Intermediate B transf should correspond to Sn(2e) with no uranium NN but with at least one uranium NNN [8].…”

“…One third of the diamagnetic Sn atoms in R x Fe 6 Sn 6 (R = rareearth) and FeSn, those on 2e and 1a sites, respectively, lie on the ab-plane, surrounded by ferromagnetically coupled Fe atoms and exhibit a non-zero magnetic hyperfine field, B transf , transferred from the neighbouring Fe atoms [3,[5][6][7]. The remaining two thirds of the Sn atoms lie between antiferromagnetically coupled Fe planes and have zero B transf at 300 K. For Dy x Fe 6 Sn 6 (x = 0.5, 1) at 4 K, however, non-zero B transf on Sn atoms with Dy nearest neighbours, NN, were reported [8].…”

Dependence of the Fe anisotropy on the Dy concentration in the DyxFe6Sn6 (0.3<x<1) compounds

“…No significant differences are observed between the zero-field cooled (ZFC) and field cooled (FC) curves, either. This agrees with the main antiferromagnetic coupling between the Fe atoms typical of FeSn and of all the A x Fe 6 X 6 whose magnetic structures are already established [7][8][9]15,19,22], as referred above. On the other hand M(T) curves of Dy 0.5 Fe 6 Sn 6 and DyFe 6 Sn 6 samples (Fig.…”

119Sn Mössbauer effect study of DyxFe6Sn6 (x=0.3, 0.5, 1) compounds

“…These short-range interactions in the structure of DyFe 6 Sn 6 , space-group Cmcm, may be described with no significant loss of accuracy using the simpler crystallographic settings of the hexagonal HfFe 6 Sn 6 -type structure [8,[10][11][12]. Therefore for all compounds Sn was considered as equally occupying 3 sites, 2c, 2d and 2e.…”

“…In FeSn and RFe 6 Sn 6 one third of Sn atoms exhibit B transf transferred from magnetically ordered Fe. B transf at the magnetically polarized Sn site, located in or close to the (0 0 1) Fe sheets, Sn(1a) in FeSn and Sn(2e) in RFe 6 Sn 6 , increase with R insertion from 5.6 T up to 24.6 T [4,6,[10][11][12]. B transf is virtually independent of R but may be lower when less than 1 R/f.u.…”