Evolution from two- to one-dimensional magnetic interactions in Cu2F5−x through electron doping by fluoride nonstoichiometry

Abstract

The copper fluoride ${\mathrm{Cu}}_{2}{\mathrm{F}}_{5}$ is a compound with two-dimensional (2D) magnetic exchange interactions between the Cu ions in the $S=1$ and $S=\frac{1}{2}$ spin states. Using ab initio calculations, we predict that the existence of 5% vacancies in the fluoride sublattice of ${\mathrm{Cu}}_{2}{\mathrm{F}}_{5}$ results in a drastic transformation of the spin state of all copper ions and the final spin states are $S=\frac{1}{2}$ and $S=0$. Consequently, the anisotropy of the magnetic interactions increases, and 1D linear chains of Cu ${d}^{9}, S=\frac{1}{2}$ ions appear. We also propose a microscopic mechanism of such a transformation of the exchange interaction via ${\mathrm{CuO}}_{6}$ octahedra elongation.