Thermal Transport and Magnetotransport Properties of CuCr1-xMgxO2with a Spin-3/2 Antiferromagnetic Triangular Lattice

Abstract

We have investigated the thermal conductivity (κ) and magnetoresistance (MR) of non-doped and hole-doped delafossite CuCrO2 with a spin-3/2 antiferromagnetic (AF) triangular sublattice. The phonon mean free path above the Néel temperature (\(T_{\text{N}}\)) deduced from κ and lattice specific heat is almost identical to the magnetic correlation length, which indicates that, for both compounds, spin fluctuation enhanced in a geometrically frustrated lattice is strongly coupled with acoustic phonon above \(T_{\text{N}}\). κ below \(T_{\text{N}}\) is significantly suppressed by Mg substitution, suggesting the introduction of some disorder into the 120° Néel state. For the hole-doped CuCr0.97Mg0.03O2, a negative MR is observed above \(T_{\text{N}}\), which is enhanced with a decrease in \(T\) toward \(T_{\text{N}}\), while a component of positive MR appears below \(T_{\text{N}}\) and the residual negative MR component is observed in a high magnetic field, indicating that spin fluctuation coupled with electrical conductivity is critically enhanced above \(T_{\text{N}}\) and remains below \(T_{\text{N}}\). These results evidence that the 120° Néel state is partially disordered by a doped itinerant hole coupled with spin fluctuation, although AF transition is certainly promoted. The dynamic partial disorder may stabilize the Néel order through an order-by-disorder mechanism.