A Mossbauer spectral study of the YCo4-xFexB compounds

The Mossbauer spectra of the YCo4-xFexB compounds, where x is 1, 2 and 3, have been measured at 78 and 295 K and reveal relatively small iron hyperfine fields of about 15 T, relatively large quadrupole interactions of about +1.0 and -1.0 mm s(-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, eta and Euler angles, theta and phi, 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.