Effect of Ni Substitution on the Structural, Magnetic, and Electronic Structure Properties of Gd 0.4 Tb 0.6 (Co 1-x Ni x ) 2 Compounds.

The comprehensive research of magnetic and electronic structure properties of the new class of Gd 0.4 Tb 0.6 (Co 1-x Ni x ) 2 compounds, crystallizing in the cubic Laves phase (C15), is reported. The magnetic study was completed with electrical resistivity and electronic structure investigations. The analysis of Arrott plots supplemented by a study of temperature dependency of Landau coefficients revealed that all compounds undergo a magnetic phase transition of the second type. Based on magnetic isotherms, magnetic entropy change ( ΔS M ) was determined for many values of the magnetic field change ( μ 0 H ), which varied from 0.1 to 7 T. For each compound, the ΔS M had a maximum around the Curie temperature. Both values of the | ΔS M max | and relative cooling power RCP parameters increased with increasing nickel content. It is shown that structural disorder upon Co/Ni substitution influences some magnetic parameters. The magnetic moment values of Co atoms determined from different methods are quantitatively consistent. From the M ( T ) dependency, the exchange integrals J RR , J RT , and J TT between rare-earths (R) and transition metal (T) moments were evaluated within the mean-field theory (MFT) approach. The experimental study of the electronic structure performed with the use of the X-ray photoelectron spectroscopy (XPS) was completed by calculations using the full-potential linearized augmented plane waves (FP-LAPW) method based on the density functional theory (DFT). The calculations explained experimentally observed changes in the XPS valence band spectra upon the Ni/Co substitution.