Understanding of magnetic behavior of the pseudo-binary Co_{2- x}Ni_xZn₁₁: in the light of crystal and electronic structures

A high-temperature synthetic approach is used to prepare a series of pseudo-binary phases-Co_2-xNi_xZn₁₁. In the structures of Co_2-xNi_xZn₁₁, the statistical distribution between Co and Ni that is suggested by compositional analysis is confirmed by combined refinements of X-ray and neutron powder diffraction (NPD) experimental data. The aforementioned phases adopt a body-centered cubic lattice with a noncentrosymmetric space group I4̄3m (217). Their crystal structures comprise two 26-atom γ-brass clusters. Each γ-cluster is made of four sequential polyhedral shells: inner tetrahedron (IT), outer tetrahedron (OT), octahedron (OH), and distorted cuboctahedron (CO). Diffraction experiments and the computations endorse that the OT site is statistically distributed by Co and Ni atoms, while the other three sites (IT, OH, and CO) are occupied by Zn atoms. The density of states (DOS) curve for Co_1.5Ni_0.5Zn₁₁ displays a similar feature as binary Co₂Zn₁₁, whereas the wide pseudo-gap is formed near E_F as Ni-concentration increases in Co_2-xNi_xZn₁₁. Bonding analysis shows that this specific atomic distribution nearly optimizes heteroatomic Co/Ni-Zn contacts in the Co_1.0Ni_1.0Zn₁₁ and Co_0.5Ni_1.5Zn₁₁. The Co_1.7Ni_0.3Zn₁₁ exhibit paramagnetic behavior, whereas Co_0.5Ni_1.5Zn₁₁ shows distinct diamagnetic behavior. With the increase in Ni concentration in the structure of Co_2-xNi_xZn₁₁, Ni atoms gradually substitute the Co atoms at OT sites; hence, magnetic characteristics change from para- to diamagnetism.