NQR study of spin-freezing in superconducting La2-xSrxCuO4: the example of x=0.06

Nuclear quadrupole resonance (NQR) La-139 and Cu-63 spin-lattice relaxation rare T-l(-1) measurements in a La1.94Sr0.06CuO4 single crystal are described. Slowing-down of Cu2+ spin fluctuations is evidenced through a dramatic increase of T-139(l)-1 on cooling. While the onset of diamagnetism occurs at T-c = 8 K, T-139(l)-1 has a peak at T-g similar or equal to 5 K, when the characteristic frequency of magnetic fluctuations reaches the NQR frequency v(Q) similar or equal to 9 MHz. in agreement with a number of previous studies, these results show that the so-called cluster spin-glass phase persists in the superconducting regime. Issues concerning the coexistence of the two phases are discussed.