Magnetic ordering in electronically phase-separated ${\text{La}}_{2-x}{\text{Sr}}_x{\text{CuO}}_{4+y}$: Neutron diffraction experiments

We present results of magnetic neutron diffraction experiments on the codoped superoxygenated ${\text{La}}_{2-x}{\text{Sr}}_x{\text{CuO}}_{4+y}$ $\left({\text{LSCO}}_{+\text{O}}\right)$ system with $x=0.09$. We find that the magnetic phase is long-range ordered incommensurate antiferromagnetic with a Néel temperature $T_N$ coinciding with the superconducting ordering temperature $T_c=40\text{K}$. The incommensurability value is consistent with a hole doping of $n_h\approx \frac{1}{8}$ but in contrast to nonsuperoxygenated ${\text{La}}_{2-x}{\text{Sr}}_x{\text{CuO}}_4$ with hole doping close to $n_h\approx \frac{1}{8}$ the magnetic-order parameter is not field dependent. We attribute this to the magnetic order being fully developed in ${\text{LSCO}}_{+\text{O}}$ as in the spin and charge ordered “stripe” compounds ${\text{La}}_{1.48}{\text{Nd}}_{0.40}{\text{Sr}}_{0.12}{\text{CuO}}_4$ and ${\text{La}}_{7/8}{\text{Ba}}_{1/8}{\text{CuO}}_4$.

Figure 1

(Color online) Scans in reciprocal space through $\left(-0.885,0.123,0\right)$ along the $K$ direction. Scans are taken above and below $T_N$ in zero applied field; the solid line is a fit to the data as explained in Sec. 4. The inset shows the peak position and scan direction.

Figure 2

(Color online) H scans through the IC peak position at various fields. The experimental data have been fit to a Gaussian on sloping background. In the figure the data points and their Gaussian fits (solid lines) are shown after subtracting their sloping background (940 cts/30 min at the peak position). All fitted Gaussian parameters are the same within error bars for the different fields.

Figure 3

(Color online) Internal magnetic moment (square root of SDW peak intensities) as a function of applied field. Closed symbols are data from RITA-II (measuring one point at the peak position) and open symbols are from SPINS (full-momentum scan fitted to a Gaussian) scaled to weighted average of RITA-II data. A constant fit to the data (solid line) is shown relative to the internal moment of LNSCO from Ref. 10 (dashed line). Shaded areas indicate the error related to the determination of the local-ordered moment from $\mu \text{SR}$.

Figure 4

(Color online) Temperature dependence of the IC SDW peak intensity at ${\mu }_{0}H=0$ (in cryostat) and ${\mu }_{0}H=13.5\text{T}$ (in magnet, after field cooling), respectively. The ${\mu }_{0}H=13.5\text{T}$ data are scaled (from the ratio of Bragg-peak intensity in the cryostat and magnet, respectively) and subtracted a constant background. The solid curve is a guide to the eyes.