Orbital Effects in Manganites

In this paper I give a short review of some properties of the colossal magnetoresistance manganites, connected with the orbital degrees of freedom. Ions Mn 3+, present in most of these compounds, have double orbital degeneracy and are strong Jahn–Teller ions, causing structural distortions and orbital ordering. Mechanisms leading to such ordering are shortly discussed, and the role of orbital degrees of freedom in different parts of the phase diagram of manganites is described. Special attention is paid to the properties of low-doped systems (doping 0.1≤x≤0.25), to overdoped systems (x>0.5), and to the possibility of a novel type of orbital ordering in optimally doped ferromagnetic metallic manganites.