Electrical resistivity, Curie temperature and band structure in Tb0.27Dy0.73(Fe1−xCox)2 intermetallics

Electrical resistivity studies performed in a wide temperature range across the complete Fe/Co substituted Tb0.27Dy0.73(Fe1−xCox)2 intermetallic series, with a borderline compound Tb0.27Dy0.73Fe2 known as Terfenol-D are presented. Parameters characterizing the dependence of resistivity on temperature, including the Debye temperature, are determined. Residual, phonon and magnetic contributions are separated from electrical resistivity. The magnetic contribution to electrical resistivity is applied to estimate Curie temperatures. Regions of weak and strong ferromagnetism of the transition metal sublattice are evidenced. The Curie temperature increases with x, approaches a maximum for x = 0.3 and reduces across the rest of the series. Some results of electronic band structure calculations using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method are also presented. A distribution function for the densities of 3d states is introduced and a formula to estimate the band splitting energy is proposed. The obtained 3d and 4s band splitting energies for iron, cobalt and average for transition metal are presented. The Curie temperature across the Tb0.27Dy0.73(Fe1−xCox)2 system is described using a formula relating to both the FLAPW calculated magnetic moments and the statistical properties of the substituted transition metal sublattice.