Low-temperature spin excitations in frustrated ZnCr2O 4 probed by high-field thermal conductivity

Abstract

The magnetoelastic excitations of spin frustrated ZnCr2O 4 are studied by the magnetic field dependence of the thermal conductivity k down to 50 mK. Above the first-order magnetostructural transition at TN,S ≈ 12.5 K, spin fluctuations are strongly coupled to acoustic phonons, leading to a glasslike dependence of k(T), up to ΘCW. In the symmetry broken phase below TN,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. © 2013 American Physical Society.