A detailed electronic phase diagram of perovskite-type oxides Sr 1-x La x FeO 3 (0 ≦ x ≦ 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 SrFeO 3 at zero field, two of them showing multipleq 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 Sr 1-x La x FeO 3 with x higher than 0.1, followed by merging to the spin/charge ordered phase with x ~ 1/3. We propose an important role of itinerant ligand holes on the emergence of multipleq states and a possible link between the third (putative singleq ) helimagnetic phase in SrFeO 3 and the spin/charge ordered phase in Sr 2/3 La 1/3 FeO 3 .

We systematically synthesized perovskite-type oxides Sr1−xCaxCoO3 containing unusually high valence Co4+ ions by a high pressure technique and investigated the effect of systematic lattice change on the magnetic and electronic properties. As the Ca content x exceeds about 0.6, the structure changes from cubic to orthorhombic, which is supported by the first-principles calculations of enthalpy. Upon the orthorhombic distortion, the ground state remains to be apparently ferromagnetic, with a slight drop of the Curie temperature. Importantly, the compounds with x larger than 0.8 show antiferromagnetic behavior, with positive Weiss temperatures and nonlinear magnetization curves at the lowest temperature, implying that the ground state is non-collinear antiferromagnetic or helimagnetic. Considering the incoherent metallic behavior and the suppression of the electronic specific heat at the high x region, the possible emergence of a helimagnetic state in Sr1−xCaxCoO3 is discussed in terms of the bandwidth narrowing and the double-exchange mechanism with the negative charge transfer energy, as well as the spin frustration, owing to the next-nearest neighbor interaction.

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