Neel to Spin-Glass-like Phase Transition versus Dilution in Geometrically Frustrated ZnCr_{2-2x}Ga_{2x}O_4

TL;DR

This study investigates the complex magnetic phase transition and the effects of nonmagnetic dilution on ZnCr2O4, revealing a near-critical tetragonal Neel phase and how dilution influences magnetic correlations and transition order.

Contribution

It provides detailed neutron scattering analysis of the spin structure and phase transition behavior in ZnCr2O4 and its diluted variants, highlighting the proximity to a critical point and the impact of dilution.

Findings

The Neel phase has multiple magnetic domains with different wave vectors.

Dilution changes the phase transition from first to second order at x=0.05.

At x=0.3, correlations become short-range but frozen spins resemble fluctuating moments in pure material.

Abstract

ZnCr2O4 undergoes a first order spin-Peierls-like phase transition at 12.5 K from a cubic spin liquid phase to a tetragonal Neel state. Using powder diffraction and single crystal polarized neutron scattering, we determined the complex spin structure of the Neel phase. This phase consisted of several magnetic domains with different characteristic wave vectors. This indicates that the tetragonal phase of ZnCr2O4 is very close to a critical point surrounded by many different Neel states. We have also studied, using elastic and inelastic neutron scattering techniques, the effect of nonmagnetic dilution on magnetic correlations in ZnCr_{2-2x}Ga_{2x}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.