MAGNETISM AND MAGNETIC FLUCTUATIONS IN LA2-XSRXCUO4 FOR X=0 (2D ANTIFERROMAGNET), X=0.04 (3D SPIN-GLASS) AND X=0.15 (SUPERCONDUCTOR)

We review recent studies of the static and dynamic magnetic fluctuatio ns in La2-xSrxCuO4. In La2CuO4(T-N = 325K) the instantaneous two-dimen sional (2D) spin correlations have been studied over the temperature r ange 340K < T greater than or equal to 820K. We find quantitative agre ement for the correlation length over the complete temperature range w ith no adjustable parameters with predictions for the 2D quantum non-l inear sigma model in the renormalized classical regime. We have carrie d out bulk magnetization measurements in La1.96Sr0.04CuO4 which has ne ither 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 performe d on homogeneous single crystals of La1.85Sr0.15CuO4 with T-c=37.3K (a t onset), higher than any previously studied single crystals. The temp erature dependence of the low energy incommensurate peak intensity at (pi(1+/-delta), pi) and (pi, pi(1+/-delta)) exhibits a pronounced maxi mum near T-c. In contrast to the results reported on lower T-c crystal s, the intensity for energies below 3.5 meV dramatically decreases as the temperature decreases below T-c, vanishing into the background bel ow similar to 15K. The behavior is consistent with predictions based o n a d(x)2(-gamma)2 superconducting order parameter.