Orbital effects in manganites

In this paper I give a short review of some properties of the colossal magn etoresistance manganites, connected with the orbital degrees of freedom. Io ns Mn3+, present in most of these compounds, have double orbital degeneracy and axe strong Jahn-Teller ions, causing structural distortions and orbita l ordering. Mechanisms leading to such ordering are shortly discussed, and the role of orbital degrees of freedom in different parts of the phase diag ram of manganites is described. Special attention is paid to the properties of low-doped systems (doping 0.1 less than or equal to x less than or equa l to 0.25), to overdoped systems (x > 0.5), and to the possibility of a nov el type of orbital ordering in optimally doped ferromagnetic metallic manga nites.