J. Phys. France 41, 1487-1494 (1980)
DOI: 10.1051/jphys:0198000410120148700

Magnetically induced quadrupole interactions and anisotropic hyperfine fields at Fe-sites in RFe2-compounds

P. Raj et S.K. Kulshreshtha

Chemistry Division, Bhabha Atomic Research Centre, Bombay 400085, India

Abstract
57Fe Mössbauer studies of HoFe2 and DyFe2 at various temperatures exhibit a small but definite asymmetry in the peak positions as well as in the peak widths. The symmetry in the line widths suggests that the magnetization deviates from [100] direction, whereas the asymmetry in the peak positions can arise either due to the existence of magnetically induced quadrupole interactions or due to the presence of an appreciable component of hyperfine field at right angle to the magnetization direction. The observed spectra have, therefore, been analysed in terms of two different approaches. In the first approach the total quadrupole interaction is assumed to consist of an axially symmetric magnetically induced part in addition to the usual term, whereas in the second approach the hyperfine coupling tensor has been assumed to be anisotropic. The sign and magnitude of quadrupole interaction terms as well as the magnitudes of the components of hyperfine coupling tensor have been estimated. Various approaches used earlier to analyse the magnitudes of anisotropic hyperfine fields have been shown to be functionally similar to our second approach of fitting. For 57Fe nuclear excited state an explicit analytical expression has been derived for an axially symmetric quadrupole splitting in terms of the observed peak positions of the nuclear Zeeman pattern.

Résumé
Les raies Mössbauer du 57Fe dans HoFe2 et DyFe 2 présentent une légère asymétrie dans leurs positions et dans leur largeur. L'asymétrie des largeurs de raies suggère que l'aimantation s'écarte de la direction [100], celle des positions peut provenir soit d'interactions quadrupolaires induites magnétiquement soit d'une composante du champ hyperfin normale à la direction d'aimantation. On a donc analysé les spectres suivant deux approches. Dans la première, on suppose que l'interaction quadrupolaire totale est la somme du terme habituel et d'un terme à symétrie axiale induit magnétiquement. Dans la seconde approche, on suppose un tenseur de couplage hyperfin anisotrope. On estime le signe et la grandeur de l'interaction quadrupolaire aussi bien que la grandeur des composantes du tenseur hyperfin. On discute les différents modèles proposés pour expliquer l'origine des champs hyperfins anisotropes.

PACS
7170C - Crystal and ligand fields.
7680 - Mössbauer effect; other gamma-ray spectroscopy.

Key words
crystal hyperfine field interactions -- dysprosium alloys -- holmium alloys -- iron alloys -- magnetisation -- Mossbauer effect -- quadrupole moments