Magnetism and magnetic fluctuations in La2-xSrxCuO4 for x=0 (2D antiferromagnet), 0.04 (3D spin glass) and x=0.15 (superconductor)

We review recent studies of the static and dynamic magnetic fluctuations in La2-xSrxCuO4. In La2CuO4(T-N = 325K) the instantaneous two-dimensional (2D) spin correlations have been studied over the temperature range 340K < T greater than or equal to 820K. We find quantitative agreement for the correlation length over the complete temperature range with no adjustable parameters with predictions for the 2D quantum non-linear sigma model in the renormalized classical regime. We have carried out bulk magnetization measurements in La1.96Sr0.04CuO4 which has neither antiferromagnetic long range order nor superconductivity. All of the features that characterize a canonical spin glass transition have been seen: irreversibility remnant magnetization and scaling behavior. Finally, neutron inelastic scattering experiments have been performed on homogeneous single crystals of La1.85Sr0.15CuO4 with T-c=37.3K (at onset), higher than any previously studied single crystals. The temperature dependence of the low energy incommensurate peak intensity at (pi(1+/-delta), pi) and (pi, pi(1+/-delta)) exhibits a pronounced maximum near T-c. In contrast to the results reported on lower T-c crystals, the intensity for energies below 3.5 meV dramatically decreases as the temperature decreases below T-c, vanishing into the background below similar to 15K. The behavior is consistent with predictions based on a d(x)2(-gamma)2 superconducting order parameter.