First-principles theory of short-range order, electronic excitations, and spin polarization in Ni-V and Pd-V alloys

Abstract

The short-range order (SRO) and long-range order (LRO) of Ni-V and Pd-V alloys are studied theoretically by a combination of first-principles calculations of Ising-like interaction energies (${\mathit{J}}_{\mathit{f}}$) with a Monte Carlo solution of the Ising Hamiltonian. We find the following: (i) There are several compositions in these alloys for which the dominant wave vectors of LRO and those of SRO do not coincide, indicating that the low-temperature (T) LRO may not always be inferred from the high-T SRO. (ii) In ${\mathrm{Ni}}_3$V and ${\mathrm{Pd}}_3$V, the density of states at the Fermi level, n(${\mathrm{\epsilon }}_{\mathit{F}}$), is much larger in L$1_2$ than in the stable D$0_{22}$ structure. This has two consequences: (a) thermal electron-hole excitations across ${\mathrm{\epsilon }}_{\mathit{F}}$ are energetically more favorable in the L$1_2$ structure and lead to a T dependence of ${\mathit{J}}_{\mathit{f}}$, and (b) magnetization stabilization is larger in L$1_2$, so spin polarization affects structural stability. As a result, (iii) calculations using T-dependent ${\mathit{J}}_{\mathit{f}}$’s are needed to obtain quantitative agreement with experimental measurements of LRO, SRO, and transition temperatures in ${\mathrm{Ni}}_{0.75}$ ${\mathrm{V}}_{0.25}$, ${\mathrm{Ni}}_{0.67}$ ${\mathrm{V}}_{0.33}$, and ${\mathrm{Pd}}_{0.75}$ ${\mathrm{V}}_{0.25}$.