Magnetism and magnetic fluctuations in La 1 − xSr xCuO 4 for x = 0 (2D antiferromagnet), 0.04 (3D spin glass) and x = 0.15 (superconductor)

Abstract

We review recent studies of the static and dynamic magnetic fluctuations in La 2 − x Sr x CuO 4. In La 2 CuO 4(T N = 325K) the instantaneous two-dimensional (2D) spin correlations have been studied over the temperature range 340 K < T ≤ 820 K. 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 La 1.96Sr 0.04CuO 4 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 La 1.85Sr 0.15CuO 4 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 ( π(1 ± δ), π) and ( π, π(1 ± δ)) exhibits a pronounced maximum near 3T 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 ~ 15K. The behavior is consistent with predictions based on a d x 2 − y 2 superconducting order parameter.