Hyperfine interactions and electronic band structure in Tb0.27Dy0.73(Fe1-xCox)2 compounds

The after-effects of Fe/Co substitution in the intermetallic series Tb0.27Dy0.73(Fe1-xCox)2, with a starting compound Tb0.27Dy0.73Fe2 known as Terfenol-D, were studied. Co substitution introduces a local area, at sub-nanoscale, with random Fe/Co neighbourhoods of the 57Fe atoms. 57Fe Moessbauer effect measurements for the intermetallic system Tb0.27Dy0.73(Fe1-xCox)2 carried out at 4.2 K evidence an [100] easy axis of magnetization. Hyperfine interaction parameters: isomer shift, a magnetic hyperfine field and a quadrupole interaction parameter were obtained from the fitting procedure of the spectra, both for the local area and for the sample as bulk. As a result of Fe/Co substitution, a Slater-Pauling type curve for the average magnetic hyperfine field vs. Co content is observed. It is found that the magnetic hyperfine fields corresponding to the local area sorted out against Co contribution in the Fe/Co neighbourhoods also create a dependence similar to a Slater-Pauling type curve. Band structure calculations using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method were performed. The experimentally determined magnetic hyperfine field correlates linearly with the weighted magnetic moment calculated per transition metal atom.