Spin-charge coupling and decoupling in perovskite-type iron oxides (Sr1-xBax)(2/3)La1/3FeO3

The perovskite-type iron oxide Sr2/3La1/3FeO3 is known to show characteristic spin-charge ordering (SCO), where sixfold collinear spin ordering and threefold charge ordering are coupled with each other. Here, we report the discovery of a spin-charge decoupling and an antiferromagnetic (AFM) state competing with the SCO phase in perovskites (Sr1-xBax)(2/3)La1/3FeO3. By comprehensive measurements including neutron diffraction, Mossbauer spectroscopy, and x-ray absorption spectroscopy, we found that the isovalent Ba2+ substitution systematically reduces the critical temperature of the SCO phase and additionally yields the spin-charge decoupling in x > 0.75. Whereas the ground state remains in the SCO phase in the whole x region, an unexpected G-type AFM phase with incoherent charge ordering or charge fluctuation appears as the high-temperature phase in the range of x > 0.75. Reflecting the competing nature between them, the G-type AFM phase partially exists as a metastable state in the SCO phase at low temperatures. We discuss the origin of the spin-charge decoupling and the emergence of the G-type AFM phase with charge fluctuation in terms of the bandwidth reduction by the Ba substitution.