Low-temperature spin excitations in frustrated ZnCr2O4probed by high-field thermal conductivity

Abstract

The magnetoelastic excitations of spin frustrated ZnCr${}_{2}$O${}_{4}$ are studied by the magnetic field dependence of the thermal conductivity $k$ down to 50 mK. Above the first-order magnetostructural transition at ${T}_{N,S}$ \ensuremath{\approx} 12.5 K, spin fluctuations are strongly coupled to acoustic phonons, leading to a glasslike dependence of $k$($T$), up to ${\ensuremath{\Theta}}_{\mathrm{CW}}$. In the symmetry broken phase below ${T}_{N,S}$, $k$ shows a dominant magnetic contribution even at the lowest temperatures probed in this work. Application of a magnetic field above 2.5 T destabilizes the spin-bond structure, leading to a sudden increase and a nonconventional temperature dependence of the thermal conductivity. The possibility of the coexistence of gapped and gapless excitations in this magnetic phase is discussed.