Anelastic spectroscopy and NQR relaxation in Sr-doped La2CuO4 around the AF percolation threshold

Anelastic spectra and La-139 NQR relaxation measurements have been carried out in La2-xSrxCuO4 (LSCO) for x around the critical value x(c) = 0.02 separating the antiferromagnetic (AF) from the cluster spin glass (CSG) phase for T --> 0. The anelastic: spectra around 10 K show step-like features common to samples pertaining to both AF and CSG phases. In the light of recent neutron scattering measurements suggesting that the spin-glass phase of LSCO with x < x corresponds to a microscopic phase separation between regions with x similar to 0 and x similar to 0.02, the rise of the elastic energy dissipation has been attributed to the movement of the domain walls within the x similar or equal to x(c) CSG regions. The spin dynamics driving the AF transition has been investigated by means of 139La NQR relaxation rate. The in-plane magnetic correlation length xi(2D) has been extracted. In spite of the vicinity to the percolation threshold, xi(2D)(x = 0.016, T) follows the temperature behavior expected in the renormalized classical regime, with spin stiffness reduced to about 0.4 of the one in pure La2CuO4. Still, the 3D transition occurs when xi(2D) is of the order of about 150 lattice steps, as in pure La2CuO4, possibly related to the presence of AF regions unaffected by the holes.