Study of atomic disorder in Ni-V alloys

Abstract

We present a pair distribution function (PDF) analysis from neutron diffraction data of the Ni1−xVx alloy in the Ni-rich regime. Such structural study aims to clarify the origin of the magnetic inhomogeneities associated with the quantum Griffiths phase close to the ferromagneticparamagnetic quantum phase transition. The PDF analysis successfully reveals the details of the structure and chemical distribution of our Ni1−xVx polycrystalline samples prepared with hightemperature annealing and rapid cooling protocol. This study confirms the expectations that all Ni1−xVx samples with 0 ≤ x ≤ 0.15 crystallize in a single phase fcc structure with some residual strain. The increase of the lattice constant and the atomic displacement parameter with Vconcentration x is consistently explained by a random occupation of V and Ni-atoms on the lattice, with a radius ratio (rV/rNi) of 1.05. Probing alternate, simple models of the local PDF, such as V-clusters or ordered structures (Ni8V, Ni3V) give inferior results compared to a random occupation. This investigation strongly supports that the magnetic clusters in the binary alloy Ni1−xVx originate from Ni-rich regions created from random occupation rather than from chemical clusters. It reveals that Ni1−xVx is one of the rare examples of a solid solution in a wide concentration regime (up to x = 0.15) persisting down to low temperatures (T = 15 K).

Structural and physical properties of Ni 1−x V x alloys around and away from quantum critical point

“…However, detailed studies around the quantum critical region are lacking. It is interesting to note that Gebretsadik et al [48] have reported the presence of residual strain in the crystal structure of Ni 1−x V x near the qcp as obtained from neutron diffraction data based on pair distribution function analysis but the local structure was found to be same as in the case of pure Ni.…”