Glassy nature of stripe ordering inLa1.6−xNd0.4Sr

Abstract

We present the results of neutron-scattering studies on various aspects of crystalline and magnetic structure in single crystals of La1.6−xNd0.4SrxCuO4 with x = 0.12 and 0.15. In particular, we have reexamined the degree of stripe order in an x = 0.12 sample. Measurements of the width for an elastic magnetic peak show that it saturates at a finite value below 30 K, corresponding to a spin-spin correlation length of 200Å. A model calculation indicates that the differing widths of magnetic and (previously reported) charge-order peaks, together with the lack of commensurability, can be consistently explained by disorder in the stripe spacing. Above 30 K (i.e., above the point at which a recent muon spin-rotation study has found a loss of static magnetic order), the width of the nominally elastic signal begins to increase. Interpreting the signal as critical scattering from slowly fluctuating spins, the temperature dependence of the width is consistent with renormalized classical behavior of a 2-dimensional anisotropic Heisenberg antiferromagnet. Inelastic scattering measurements show that incommensurate spin excitations survive at and above 50 K, where the elastic signal is neglible. Given that the stripe order is believed to be pinned by the low-temperature tetragonal (LTT) crystal structure, we have also investigated the transition near 70 K from the low-temperature orthorhombic (LTO) structure. We show that our x = 0.12 crystal passes through an intervening less-orthorhombic phase, before reaching the LTT at ∼ 40 K, whereas the x = 0.15 crystal goes directly from LTO to LTT, with coexistence of the two phases over a range of ∼ 7 K. Sharp Bragg peaks in the LTT phase of the x = 0.15 crystal indicate a domain size of > ∼ 1000Å, with no obvious evidence for LTO domains; hence, the coexistence of stripe order and superconductivity in this sample cannot be explained by a mixture of crystalline phases. Finally, we present scattering evidence for small LTT-like domains in the LTO phase of the x = 0.15 sample. A correlation between the volume fraction of such domains and deviations of in-plane resistivity from linear T dependence suggest that charge stripes interact with these domains within the LTO matrix.75.50. Ee, 75.30.Fv, 71.45.Lr, 71.27+a

Evidence for an incommensurate magnetic resonance inLa2−xSrxCuOTranquada1, Lee2, Yamada3 et al. 2004Phys. Rev. BSelf Cite858972View full textAdd to dashboardCite

“…Finally, we note that the low-energy magnetic excitations in the normal state of La 2−x Sr x CuO 4 look very much like those observed 48,49 in stripe-ordered La 1.48 Nd 0.4 Sr 0.12 CuO 4 . In the latter system, one interprets the incommensurate excitations as spin waves of the magnetically ordered system.…”

Similar glassy features in theL139aNMR response of pure and disorderedLa1.88Mitrović1, Julien2, Vaulx3 et al. 2008Phys. Rev. B8211980View full textAdd to dashboardCite

“…Glassiness is, however, also present in materials where stripe order is well-defined and relatively long range [8]. Furthermore, from the T dependence of an average 139 La spin-lattice relaxation rate T −1 1 , Curro et al [12] concluded that the distribution of magnetic correlation times (Color online) Sketch of the phase diagram of La2−xSrxCuO4.…”

“…Indeed, the temperature of magnetic freezing, T g , in La 2−x Sr x CuO 4 is peaked in the vicinity of x 1 8 ( Fig. 1), and neutron scattering studies [5,6,7] reveal long-range antiferromagnetic order with the same typical modulation as in the materials presenting direct evidence for charge stripe order [8]. Another approach relies on electronic and magnetic inhomogeneities generated by quenched disorder [9].…”

Spin dynamics and ordering of a cuprate stripe antiferromagnet

“…Experimental evidence for stripe correlations has been provided by neutron studies in Nd-doped La 1.875 Sr 0.125 CuO 4 and in other cuprates and nickelates. 1,2 The spatial organization of the stripe structures is a subject of much debate. [3][4][5][6][7][8] Stripe formation is characterized by the temperatures of charge (T charge ) and spin T spin ordering with T charge ϾT spin .…”