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

Abstract

57Fe Mossbauer 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.