Spin dynamics in hole-doped two-dimensional S=1/2 Heisenberg antiferromagnets: Cu-63 NQR relaxation in La2-xSrxCuO4 for x <= 0.04

The effects on the correlated Cu2+ S = 1/2 spin dynamics in the paramagneti c phase of La2-xSrxCuO4 (for x less than or similar to 0.04) due to the inj ection of holes are studied by means of Cu-63 NQR spin-lattice relaxation t ime T-1 measurements. The results are discussed in the framework of the con nection between T-1 and the in-plane magnetic correlation length xi(2D)(x, T). It is found that at high temperatures the system remains in the renorma lized classical regime, with a spin stiffness constant rho(s)(x) reduced by small doping to an extent larger than the one due to Zn doping. For x grea ter than or similar to 0.02 the effect of doping on rho(s)(x) appears to le vel off. The values for rho(s)(x) derived from T-1 for T greater than or si milar to 500 K are much larger than the ones estimated from the temperature behavior of sublattice magnetization in the ordered phase (T less than or equal to T-N). It is argued that these features are consistent with the hyp othesis: of formation of stripes of microsegregated holes.