A Mössbauer spectral study of the YCo_4-xFe_xB compounds

The Mössbauer spectra of the YCo_4-xFe_xB compounds, where x is 1, 2 and 3, have been measured at 78 and 295K and reveal relatively small iron hyperfine fields of about 15T, relatively large quadrupole interactions of about +1.0 and -1.0mms^-1 and very different spectra for YCo₃FeB and YCo₂Fe₂B as compared with YCoFe₃B. As a consequence, the spectra have been fitted with a full Hamiltonian by adjusting the hyperfine parameters of the iron 2c and 6i sites found in these compounds. The fits have used an asymmetry parameter, η, and Euler angles, and , that relate the hyperfine field to the iron electric field gradient axes of each iron site in an orientation that is consistent with the structural and magnetic properties of the site. The fits indicate that the relative areas of the spectral components assigned to the two iron 2c and 6i sites are in agreement with the iron occupancy of the sites as determined by neutron diffraction. The results of the fits also indicate both that the full Hamiltonian approach is required for physically reasonable spectral fits and that the small observed fields result from the presence of large orbital contributions which subtract from the Fermi contact contributions to the magnetic hyperfine fields of the two sites.