Complete phase diagram of ${\mathrm{Sr}}_{1–x}{\mathrm{La}}_x\mathrm{Fe}{\mathrm{O}}_3$ with versatile magnetic and charge ordering

A detailed electronic phase diagram of perovskite-type oxides ${\mathrm{Sr}}_{1–x}{\mathrm{La}}_x\mathrm{Fe}{\mathrm{O}}_3$ ($0\leqq x\leqq 0.5$) was established by synchrotron x-ray diffraction, magnetization, and transport measurements for polycrystalline samples synthesized by a high-pressure technique. Among three kinds of helimagnetic phases in $\mathrm{SrFe}{\mathrm{O}}_3$ at zero field, two of them showing multiple-$\mathit{q}$ helimagnetic spin textures tend to rapidly disappear in cubic symmetry upon the La substitution with $x$ less than 0.1, which accompanies the loss of metallic nature. On the other hand, the third helimagnetic phase apparently remains robustly in ${\mathrm{Sr}}_{1–x}{\mathrm{La}}_x\mathrm{Fe}{\mathrm{O}}_3$ with $x$ higher than 0.1, followed by merging to the spin/charge ordered phase with $x\sim 1/3$. We propose an important role of itinerant ligand holes on the emergence of multiple-$\mathit{q}$ states and a possible link between the third (putative single-$\mathit{q}$) helimagnetic phase in $\mathrm{SrFe}{\mathrm{O}}_3$ and the spin/charge ordered phase in ${\mathrm{Sr}}_{2/3}{\mathrm{La}}_{1/3}\mathrm{Fe}{\mathrm{O}}_3$.

Figure 1

(a) Synchrotron powder XRD patterns for ${\mathrm{Sr}}_{1–x}{\mathrm{La}}_x\mathrm{Fe}{\mathrm{O}}_3$ with selected compositions at room temperature and (b) the magnified view around 2θ of 17 °. Rietveld refinement plots of synchrotron XRD data for ${\mathrm{Sr}}_{1–x}{\mathrm{La}}_x\mathrm{Fe}{\mathrm{O}}_3$ with (c) $x=0.25$ and (d) $x=0.45$. The red dots, green lines, blue lines, and vertical green tick marks represent observed patterns, calculated patterns, differences between observed and calculated intensities, and Bragg reflection points, respectively. The insets in (c,d) show the crystal structure of $x=0.25$ and $x=0.45$, respectively.

Figure 2

$x$ dependences of (a) pseudocubic lattice constant $a_{\mathrm{cubic}}$, (b) Fe-O bond length, (c) Fe-O-Fe bond angle, and (d) bond valence sum (BVS) of Fe ion. $a_{\mathrm{cubic}}$ for the rhombohedral compounds with $x\geqq 0.33$ was calculated by $a_{\mathrm{cubic}}={\left(V/6\right)}^{1/3}$ (V: volume of the rhombohedral unit cell). The broken line in (d) corresponds to the formal valence predicted from the chemical composition.

Figure 3

(a–c) Temperature dependence of magnetic susceptibility for ${\mathrm{Sr}}_{1–x}{\mathrm{La}}_x\mathrm{Fe}{\mathrm{O}}_3$ measured at 0.1 T. The measurements were performed on field cooling (FC), on warming after field cooling at 0.1 T (FW), and on warming after zero-field cooling (ZFC). (d) Temperature dependence of resistivity for ${\mathrm{Sr}}_{1–x}{\mathrm{La}}_x\mathrm{Fe}{\mathrm{O}}_3$ measured on cooling and heating at 0 T. The closed triangles in (b,d) denote the onset of spin/charge ordering.

Figure 4

Temperature dependence of (a) magnetic susceptibility and (b,c) resistivity for $0\leqq x\leqq 0.1$ measured on cooling and warming runs. Temperature derivative of (d) magnetic susceptibility and (e,f) resistivity for $0\leqq x\leqq 0.1$. The solid and broken lines in (d,e) show the data for warming and cooling runs, respectively. The closed and open triangles correspond to the transition temperatures separating the different helimagnetic phases (phases I–III) determined from the data for warming and cooling runs, respectively. In (d,e), the data are offset for clarity. For $x=0.02$, the transition between phases I and II is apparent only in the resistivity data.

Figure 5

(a–c) Magnetic field dependence of magnetization (left axis) and magnetization divided by magnetic field (right axis) at 5 K for selected compositions in $0\leqq x\leqq 0.1$. (d–i) Magnetoresistance, defined as $\mathrm{\Delta }\rho \left(B\right)/\rho \left(0\right)\left[\mathrm{\Delta }\rho \left(B\right)=\rho \left(B\right)–\rho \left(0\right)\right]$, at 5 K (d–f) and 100 K (g–i).

Figure 6

(a) Composition dependence of magnetic susceptibility at $T=5\mathrm{K}$ measured at $B=0.1\mathrm{T}$ after field cooling (FC) and zero-field cooling (ZFC). (b) Composition dependence of resistivity at $T=60\mathrm{K}$ measured on a warming run at $B=0\mathrm{T}$. (c) Phase diagram for ${\mathrm{Sr}}_{1–x}{\mathrm{La}}_x\mathrm{Fe}{\mathrm{O}}_3$. The red circles and blue crosses represent the transition temperatures determined by the warming runs of magnetization and resistivity measurements, respectively. Phases I–III are helimagnetic phases with different spin spirals. (d) Schematic spin image of the magnetic structures for phases I–III and the spin/charge ordered phase. These schematics are drawn assuming the presence of an external magnetic field along the [111] axis.