Electronic phase separation and other novel phenomena and properties exhibited by mixed-valent rare-earth manganites and related materials

Abstract

Transition metal oxides, such as the mixed-valent rare-earth manganites Ln (1Kx) A x MnO 3 (Ln, rare-earth ion, and A, alkaline-earth ion), show a variety of electronic orders with spatially correlated charge, spin and orbital arrangements, which in turn give rise to many fascinating phenomena and properties. These materials are also electronically inhomogeneous, i.e. they contain disjoint spatial regions with different electronic orders. Not only do we observe signatures of such electronic phase separation in a variety of properties, but we can also observe the different 'phases' visually through different types of imaging. We discuss various experiments pertaining to electronic orders and electronic inhomogeneities in the manganites and present a discussion of theoretical approaches to their understanding. It is noteworthy that the mixed-valent rare-earth cobaltates of the type Ln (1Kx) A x CoO 3 also exhibit electronic inhomogeneities just as the manganites.

Long range electronic phase separation in CaFe3O5

“…Charge ordering in one of the two low temperature phases is clearly a key driver for the long range electronic phase separation in CaFe 3 O 5 and perovskite type oxides 15 although in CaFe 3 O 5 this leads to the formation of orbital molecules 16 , more complex electronic objects than simple localised-charge ions. However, phase separation in CaFe 3 O 5 occurs without a change of lattice symmetry in either component, demonstrating that strain variations within a given lattice are sufficient to drive long range segregation.…”

Mixed valence: origins and developments

“…When analogous situations are found in infinite lattice oxides, such as perovskites, we find many fascinating phenomena arising from the different distributions of the two oxidation states, coupled with the interaction between localized and delocalized electrons. The latter gives rise to the property of 'colossal magneto-resistance', as Raveau (2008) and Shenoy & Rao (2008) reveal in this discussion.…”

In My Element: Oxygen

“…[3] The discoveryo fc olossal magnetoresistance in rare earth manganites of the typeL a 1Àx Ca x MnO 3 which show both orbital In celebration of the InternationalY ear of the Periodic Table. and charge-ordering led to av ariety of investigationsa nd to the observation of the phenomenon of electronic phase separation. [4] We observed major effects of phase separation in Nd 0.5 Sr 0.5 MnO 3 ,w hich is ferromagnetic at ordinary temperatures, and occurs in three phases (FM + 2AFMs)a tl iquid helium temperatures. Is tarted workingo nm ultiferroics in the 1990's, the well-known examples being BiFeO 3 and YMnO 3 .…”