HIGH-TEMPERATURE SPIN DYNAMICS IN LA2-DELTA-SR-DELTA-CUO4

Motivated by magnetic-resonance experiments for La2-deltaSrdeltaCuO4 a t temperatures up to 900 K, we calculate the spin-lattice relaxation r ate 1/T1 for Cu nuclei within the Gaussian approximation at high tempe ratures (T greater than or similar to J/2) for the S = 1/2 Heisenberg antiferromagnet and at T = infinity for the t-J model, taking into acc ount the transferred as well as the direct hyperfine coupling. For the Heisenberg model, including the transferred coupling weakens the temp erature dependence of 1/T1 and leads to better agreement with the expe rimental data than the calculation that only includes direct hyperfine coupling. For the t-J model, the infinite-temperature 1/T1 within the Gaussian approximation decreases markedly upon doping. We propose a n on-Gaussian form for the spectral density that is consistent with the exact moments and more in accord with the experiments, which find 1/T1 nearly independent of delta at T almost-equal-to J/2.