Magnetic heat transport in R2CuO4 (R=La, Pr, Nd, Sm, Eu, and Gd)

We have studied the thermal conductivity kappa on single crystalline samples of the antiferromagnetic monolayer cuprates R2CuO4 with R=La, Pr, Nd, Sm, Eu, and Gd. For a heat current within the CuO2 planes, i.e., for kappa(ab) we find high-temperature anomalies around 250 K in all samples. In contrast, the thermal conductivity kappa(c) perpendicular to the CuO2 planes, which we measured for R=La, Pr, and Gd, shows a conventional temperature dependence as expected for a purely phononic thermal conductivity. This qualitative anisotropy of kappa(i) and the anomalous temperature dependence of kappa(ab) give evidence for a significant magnetic contribution kappa(mag) to the heat transport within the CuO2 planes. Our results suggest, that a large magnetic contribution to the heat current is a common feature of single-layer cuprates. We find that kappa(mag) is hardly affected by structural instabilities, whereas already weak charge carrier doping causes a strong suppression of kappa(mag).