Low-dimensional Spin 1/2 Antiferromagnets

63 Cu and 170 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments are reported on copper-oxide compounds related to high tem-perature superconductors that are nearly ideal realizations of spin 1/2 Heisenberg antiferromagnets with different geometries of the magnetic interactions: 1 dimen-sional spin chains, 2 dimensional planes, two coupled chains (two-leg ladder), and three coupled chains (three-leg ladder). Comparison of the spin-lattice relaxation rate, 1/T 1, for 6 3Cu and 170 reveals the wave-vector, q, dependence of low-energy magnetic fluctuations, and 1/T 2G, the Gaussian spin-spin relaxation rate provides in-formation about the electron spin correlation length,. In the Id material, Sr 2 CuO 3,171/T 1 (q = 0) oc aT + bT 2 over the whole temperature range 10 to 700 K. Frequency dependence measurements show that diffusive contributions dominate T1 (q r 0) for the double chain id material, SrCuO 2. For the undoped 2d copper oxide material, Sr 2 CuO 2 Cl2, we demonstrate that 170 1/T 1 measures the spin wave damping in the undoped antiferromagnet for short wavelengths. We find that the spin wave damping is small, clarifying one of the unique properties of these 2d copper-oxide antiferromag