Thermal properties of single-crystal La2CuO/sub 4-//sub Δ/

We report measurements of the thermal conductivity, Raman spectrum, magnetic susceptibility, and specific heat of a single crystal of La2CuO/sub 4-//sub Δ/ from room temperature down to 10 K. We observe a sharp kink in the heat conductivity near 250 K in the [001] direction and a broader anomaly in the range 130--200 K in the [110] direction. These features have been correlated, in terms of a strongly temperature-dependent photon-magnon scattering mechanism, with changes in the magnetic structure as identified through susceptibility studies. These results differ substantially from experiments on sintered samples, which show a thermal conductivity more reminiscent of a tunneling system. It is suggested that the amorphouslike behavior of the sintered materials is an artifact of their rather poor crystalline nature, which masks the intrinsic effects associated with the single crystal as reported here