NQR Study of Spin-Freezing in Superconducting La2-xSrxCuO4: The Example of x=0.06

Abstract

NQR 139La and 63Cu spin-lattice relaxation rate (1/T_1) measurements in a La1.94Sr0.06CuO4 single crystal are described. Slowing-down of Cu2+ spin fluctuations is evidenced through a dramatic increase of 139La 1/T_1 on cooling. While the onset of diamagnetism occurs at Tc=8 K, 1/^{139}T_1 has a peak at Tg~5 K, when the characteristic frequency of magnetic fluctuations reaches the NQR frequency nu_Q~19 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.

Submitted to Applied Magnetic Resonance (Proceedings of the specialized colloque Ampere "EPR, NMR, NQR in Solid State Physics: Recent Trends") 6 pages incl. 1 figure