Charge ordering in the rare earth manganates: the experimental situation

Charge-ordered phases of rare earth manganates are novel manifestations ari sing from interactions between the charge carriers and phonons, giving rise to the localization of carriers at specific sites in the lattice below a c ertain temperature. Accompanying this phenomenon, the Mn3+ (e(g)) orbitals and the associated lattice distortions also exhibit long range ordering(orb ital ordering). What makes the manganates even more interesting is the occu rrence of complex spin ordering related to anisotropic magnetic interaction s. In this article, we discuss the emerging scenario of charge-ordered rare earth manganates in the light of specific case studies and highlight some of the new experimental findings related to spin, orbital and charge orderi ng. We also examine features such as the charge stripes and phase separatio n found experimentally in these materials, and discuss the factors that aff ect charge-ordering such as the size of A-site cations and magnetic and ele ctric fields, as well as isotopic and chemical substitutions.