Electronic structure and related thermal and magnetic properties of some ternary Invar alloys

We present first-principles electronic structure calculations of some face-centered-cubic disordered ternary Invar alloys, using the tight-binding linearized muffin-tin orbital method combined with the coherent-potential approximation (TB-LMTO-CPA). We calculate the total energies, equilibrium lattice parameters, bulk moduli, magnetic moments, and hyperfine fields for Fe-Ni-Co, Fe-Ni-Pd, and Fe-Ni-Pt Invar alloys. Charge densities at the nuclei, which can be used to interpret the results of isomer shift experiments in these alloys, are also presented. The effects of systematic Co, Pd, and Pt substitution in binary ${\mathrm{Fe}}_{65}{\mathrm{Ni}}_{35}$ alloy on the above properties are carefully examined. We examine the high moment to low moment transition by varying the concentration of Fe. Total-energy curves as a function of the lattice parameter show two distinct minima corresponding to the ferromagnetic (high moment and high volume) and nonmagnetic (zero moment and low volume) states. By using the Debye-Grüneisen model, we calculate thermal-expansion coefficients of these alloys near the Invar compositions. The results are in qualitative agreement with the experimental trend. Finally, we present results for the effective exchange coupling parameter in these alloys following the LMTO-CPA treatment of Liechtenstein et al. [J. Magn. Magn. Mater. 67, 65 (1987)]. Comparison of the calculated quantities with available experimental results is provided, wherever appropriate and feasible.