Hyperfine interactions in Tb0.27Dy0.73(Fe1-xCox)2 compounds at 77 K

The synthesis of materials, crystal structure and 57Fe Moessbauer effect studies at 77 K were performed for intermetallics Tb0.27Dy0.73(Fe1-xCox)2. The starting compound Tb0.27Dy0.73Fe2 of this Fe/Co substituted series is known as Terfenol-D. XRD measurements evidence a pure cubic Laves phase C15, MgCu2-type. The determined unit cell parameter decreases across the series. Co substitution introduces a local area, in the subnanoscale, with random Fe/Co neighbourhoods of the 57Fe atoms. Moessbauer effect spectra for the Tb0.27Dy0.73(Fe1-xCox)2 series collected at 77 K consist of a number of locally originated subspectra due to random composition of Fe and Co atoms in the nearest neighbourhood. Hyperfine interaction parameters: isomer shift, 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 in the Tb0.27Dy0.73(Fe1-xCox)2 series 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 the Slater-Pauling type curve. (authors)