Spin-charge coupling and decoupling in perovskite-type iron oxides (Sr${}_{1-x}$Ba${}_x$)${}_{2/3}$La${}_{1/3}$FeO${}_3$

Abstract

The perovskite-type iron oxide Sr${}_{2/3}$La${}_{1/3}$FeO${}_3$ 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 (Sr${}_{1-x}$Ba${}_x$)${}_{2/3}$La${}_{1/3}$FeO${}_3$. By comprehensive measurements including neutron diffraction, M$\ddot{o}$ssbauer spectroscopy, and x-ray absorption spectroscopy, we found that the isovalent Ba${}^{2+}$ 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.

arXiv comment7 pages, 5 figures

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