Eur. Phys. J. B 18, 49-54 (2000)
https://doi.org/10.1007/s100510070076

Anelastic relaxation and ¹³⁹La NQR in La_2-xSr_xCuO₄ around the critical Sr content x = 0.02

¹ Dipartimento di Fisica "A. Volta"and Unitá INFM di Pavia, Via Bassi 6, 27100 Pavia, Italy
² Dipartimento di Fisica, Universitá di Roma "La Sapienza"and Unitá INFM, P.zale A. Moro 2, 00185 Roma, Italy
³ CNR, Area di Ricerca di Roma-Tor Vergata, Istituto di Acustica "O.M. Corbino"and Unitá INFM, Via del Fosso del Cavaliere, 00133 Roma, Italy

Received: 18 May 2000
Revised: 11 July 2000
Published online: 15 November 2000

Abstract

Anelastic relaxation and ¹³⁹LaNQR relaxation rates in La_2-xSr_xCuO₄ 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 phase diagram of La_2-xSr_xCuO₄ at the boundary between the antiferromagnetic (AF) and the spin-glass phase (x= 0.02) could be more complicate than previously thought, with a transition to a quasi-long range ordered state at K, as indicated by neutron scattering data. On the other hand, the ¹³⁹LaNQR spectra are compatible with a transition to an AF phase around K, in agreement with the phase diagram commonly accepted in literature. In this case the peaks in NQR and anelastic relaxation rates around 150 K and 80 K respectively in La_1.98Sr_0.02CuO₄, yield the first evidence of freezing process involving simultaneously lattice and spin excitations, possibly corresponding to motion of charged stripes.