Néel to spin-glass-like phase transition versus dilution in geometrically frustratedZnCr2−2xGa2xO4

Abstract

$\mathrm{Zn}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$ undergoes a first order spin-Peierls-like phase transition at $12.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ from a cubic spin liquid phase to a tetragonal N\'eel state. [S.-H. Lee, C. Broholm, T. H. Kim, W. Ratcliff II, and S-W. Cheong, Phys. Rev. Lett. 84, 3718 (2000)]. Using powder diffraction and single crystal polarized neutron scattering, we determined the complex spin structure of the N\'eel phase. This phase consisted of several magnetic domains with different characteristic wave vectors. This indicates that the tetragonal phase of $\mathrm{Zn}{\mathrm{Cr}}_{2\ensuremath{-}2x}{\mathrm{Ga}}_{2x}{\mathrm{O}}_{4}$ is very close to a critical point surrounded by many different N\'eel states. We have also studied, using elastic and inelastic neutron scattering techniques, the effect of nonmagnetic dilution on magnetic correlations in $\mathrm{Zn}{\mathrm{Cr}}_{2\ensuremath{-}2x}{\mathrm{Ga}}_{2x}{\mathrm{O}}_{4}$ ($x=0.05$ and 0.3). For $x=0.05$, the magnetic correlations do not change qualitatively from those in the pure material, except that the phase transition becomes second order. For $x=0.3$, the spin-spin correlations become short range. Interestingly, the spatial correlations of the frozen spins in the $x=0.3$ material are the same as those of the fluctuating moments in the pure and the weakly diluted materials.