Charge ordering in doped manganese oxides: Lattice dynamics and magnetic structure

Based on the Hamiltonian of small polarons with strong nearest-neighbor repulsion, we have investigated the charge-ordering phenomena observed in half-doped manganites ${\mathrm{R}}_{1\mathrm{/}2}$${\mathrm{A}}_{1\mathrm{/}2}$${\mathrm{MnO}}_{3}$. We have explored possible consequences of the charge-ordering phase in the half-doped manganites. First, we have studied the renormalization of the sound velocity around ${\mathrm{T}}_{\mathrm{CO}}$, considering the acoustic phonons coupled to the electrons participating in the charge ordering. Second, we have found an antiferromagnetic phase induced by the charge ordering, and discussed its role in connection with the specific CE-type antiferromagnetic structure observed in half-doped manganites.