Atomic disorder in Ni-V alloys studied using neutron scattering

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 ferromagnetic-paramagnetic quantum phase transition. The PDF analysis successfully reveals information about structural and atomic disorder comparing short-range correlations in our Ni1-xVx polycrystalline samples prepared with high-temperature 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 lattice constant and the atomic displacement parameter increase with V concentration x. Both changes are consistently explained by a random occupation of V and Ni atoms on the lattice sites with small displacements due to the different atomic radii with ratio (rV/rNi) of 1.05. Probing alternate, simple models of the local PDF, such as V clusters or ordered structures (Ni8V, Ni3V), gives inferior results compared to a random occupation. This investigation strongly supports the magnetic clusters in the binary alloy Ni1-xVx originating from Ni-rich regions created from random occupation rather than from chemical clusters. The simple tests already demonstrate 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).