Spin dynamics in hole-doped two-dimensional S = 1/2 Heisenberg antiferromagnets: ⁶³Cu NQR relaxation in La_2-xSr_xCuO₄ for x ≤ 0.04

Abstract:

The effects on the correlated Cu²⁺ S = 1/2 spin dynamics in the paramagnetic phase of La_2-xSr_xCuO₄ (for ≲) due to the injection of holes are studied by means of ⁶³Cu NQR spin-lattice relaxation time T₁ measurements. The results are discussed in the framework of the connection between T₁ and the in-plane magnetic correlation length ${\xi _{2D}}(x,T)$. It is found that at high temperatures the system remains in the renormalized classical regime, with a spin stiffness constant ρ_S(x) reduced by small doping to an extent larger than the one due to Zn doping. For x ≲ 0.02 the effect of doping on ρ_S(x) appears to level off. The values for ρ_S(x) derived from T₁ for T ≲ 500 K are much larger than the ones estimated from the temperature behavior of sublattice magnetization in the ordered phase (T ≤ T_N). It is argued that these features are consistent with the hypothesis of formation of stripes of microsegregated holes.