Local order and frustration in the geometrically frustrated spinelsCd1−xZnxV2O4

Abstract

Orbitally degenerate frustrated spinels, ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$, with $0\ensuremath{\leqslant}x\ensuremath{\leqslant}1$ were investigated using elastic and inelastic neutron scattering techniques. In the end members with $x=0$ and 1, a tetragonal distortion $(c<a)$ has been observed upon cooling mediated by a Jahn-Teller distortion that gives rise to orbital ordering. This leads to the formation of spin chains in the $ab$-plane that upon further cooling, N\'eel ordering is established due to interchain coupling. In the doped compositions, however, the bulk susceptibility, $\ensuremath{\chi}$, shows that the macroscopic transitions to cooperative orbital ordering and long-range antiferromagnetic ordering are suppressed. However, the inelastic neutron scattering measurements suggest that the dynamic spin correlations at low temperatures have similar one-dimensional characteristics as those observed in the pure samples. The pair density function analysis of neutron diffraction data shows that the local atomic structure does not become random with doping but rather consists of two distinct environments corresponding to $\mathrm{Zn}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$ and $\mathrm{Cd}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$. This indicates that short-range orbital ordering is present which leads to the one-dimensional character of the spin correlations even in the low temperature cubic phase of the doped compositions.