Neutron scattering study on La1.9Ca1.1Cu2O6+delta and La1.85Sr0.15CaCu2O6+delta

TL;DR

This neutron scattering study investigates the magnetic and structural properties of La2-x(Ca,Sr)xCaCu2O6+delta crystals, revealing how doping influences antiferromagnetic order, structural transitions, and superconductivity in high-temperature superconductors.

Contribution

The paper provides detailed neutron scattering data on Ca- and Sr-doped La2CaCu2O6+delta crystals, highlighting the relationship between structural transitions and magnetic order in these materials.

Findings

Ca-doped crystal exhibits long-range antiferromagnetic order

Sr-doped crystal shows short-range antiferromagnetic order and weak superconductivity

Structural transition from tetragonal to orthorhombic symmetry occurs in both crystals

Abstract

We present neutron scattering data on two single crystals of the high temperature superconductor La2-x(Ca,Sr)xCaCu2O6+delta. The Ca0.1-doped crystal exhibits a long-range antiferromagnetically ordered ground state. In contrast, the Sr0.15-doped crystal exhibits short-range antiferromagnetic order as well as weak superconductivity. In both crystals antiferromagnetic correlations are commensurate; however, some results on the Ca0.1-doped crystal resemble those on the spin-glass phase of La2-xSrxCuO4, where magnetic correlations became incommensurate. In addition, both crystals show a structural transition from tetragonal to orthorhombic symmetry. Quite remarkably, the temperature dependence and correlation length of the magnetic order is very similar to that of the orthorhombic distortion. We attribute this behavior to an orthorhombic strain-induced inter-bilayer magnetic coupling, which triggers the antiferromagnetic order. The large size of the crystals made it also possible to study the magnetic diffuse scattering along rods perpendicular to the CuO2 planes in more detail. For comparison we show X-ray diffraction and magnetization data. In particular, for the Ca0.1-doped crystal these measurements reveal valuable information on the spin-glass transition as well as a second anomaly associated with the Neel transition.