Anelastic relaxation and La-139 NQR in La2-xSrxCuO4 around the critical Srcontent x=0.02

Anelastic relaxation and (139)LaNQR relaxation rates in La2-xSrxCuO4 for Sr content around 2 and 3 percent are discussed in terms of spin and lattice excitations and of the related ordering processes. It is argued how the pha se diagram of La2-xSrxCuO4 at the boundary between the antiferromagnetic (A F) and the spin-glass phase (x = 0.02) could be more complicate than previo usly thought, with a transition to a quasi-long range ordered state at T si milar or equal to 150 K, as indicated by neutron scattering data. On the ot her hand, the (139)LaNQR spectra are compatible with a transition to an AF phase around T similar or equal to 50 K, in agreement with the phase diagra m commonly accepted in literature. In this case the peaks in NQR and anelas tic relaxation rates around 150 K and 80 K respectively in La1.98Sr0.02CuO4 , yield the first evidence of freezing process involving simultaneously lat tice and spin excitations, possibly corresponding to motion of charged stri pes.