Evidence for Charge Orbital and Spin Stripe Order in an Overdoped Manganite

Overdoped ${\mathrm{La}}_{0.42}{\mathrm{Sr}}_{1.58}{\mathrm{MnO}}_4$ exhibits a complex ordering of charges, orbitals, and spins. Neutron diffraction experiments reveal three incommensurate and one commensurate order parameters to be tightly coupled. The position and the shape of the distinct superstructure scattering as well as higher-order signals are inconsistent with a harmonic charge and spin-density-wave picture but point to a stripe arrangement in which ferromagnetic zigzag chains are disrupted by excess ${\mathrm{Mn}}^{4+}$.

Figure 1

Temperature dependence of magnetization for a field of 1 T applied parallel to the $ab$ planes for $x=0.5$ and 0.58 (a). The inset presents the in-plane electric resistivity for $x=0.58$ (b). For ${\mathrm{La}}_{0.42}{\mathrm{Sr}}_{1.58}{\mathrm{MnO}}_4$, characteristic superstructure reflections increase in intensity at the transition temperatures into the COO state and into the AFM state, respectively (c).

Figure 2

Distribution of structural and magnetic scattering in the $(h,k,0)$ plane for ${\mathrm{La}}_{0.5}{\mathrm{Sr}}_{1.5}{\mathrm{MnO}}_4$ and ${\mathrm{La}}_{0.42}{\mathrm{Sr}}_{1.58}{\mathrm{MnO}}_4$. For $x=0.5$ superstructure reflections refer to the charge (green circles), orbital (gray triangles), and magnetic ordering (${\mathrm{Mn}}^{3+}$: dotted circles; ${\mathrm{Mn}}^{4+}$ red squares) (a). The ordered state for $x=0.58$ is governed by an incommensurate ordering of charge, orbital, and magnetic ordering of ${\mathrm{Mn}}^{3+}$ (b). Slightly above the Néel temperature $T_N$, the magnetic superstructure reflections vanish but a diffuse magnetic signal is still visible (c). At room temperature, diffuse signals exist around the Bragg reflections $\mathbf{Q}=(0,2,0)$ and $\mathbf{Q}=(0,1,0)$ (d). Contaminations from a crystallite and from the Al sample holder are covered in blue color.

Figure 3

Single-counter scans across the different superstructure peaks; intensities were scaled to the low-temperature peak heights in the flat-cone data. Satellites referring to the charge ordering (a) are displaced twice as much as those of orbital ordering (b) and of ${\mathrm{Mn}}^{3+}$ spin ordering (c), respectively. Reflections related to the magnetic ordering of ${\mathrm{Mn}}^{4+}$ appear at commensurate positions (d). The lines in (a) and (b) correspond to fits with Gaussian, while the lines referring to magnetic ordering in (c) and (d) correspond to fits with Lorentzians. The data in (c) are taken on G4.3, while data in (a), (b), and (d) are taken on 3.T1 (horizontal bars give the respective resolution).

Figure 4

Sketch of charge, orbital, and spin order for ${\mathrm{La}}_{0.42}{\mathrm{Sr}}_{1.58}{\mathrm{MnO}}_4$ (a). Red circles represent ${\mathrm{Mn}}^{3+}$ and green circles ${\mathrm{Mn}}^{4+}$. A single domain of zigzag chains propagating in the [110] direction is shown. The excess lines of ${\mathrm{Mn}}^{4+}$ are displayed on a green background. The Fourier transformations superposed for all domains (b) agree with the experimental map obtained at $T=2\mathrm{K}$ (c) [25]. Note that the intensity at the position $Q=(1,1,0)$ in (c) is a Bragg peak.