Electronic Phase Separation in Magnetic Materials

A review of the basic concepts and mechanisms related to the electronic phase separation and the formation of nanoscale inhomogeneities in magnetic materials is given. We put the main emphasis onto strongly correlated electron systems such as manganites, where phase separation occurs due to the competition of ferro- and antiferromagnetic states, as well as cobaltites, where the spin-state transitions play an important role. Special attention is paid to the mechanism of phase separation related to the imperfect nesting of sheets of the Fermi surface, which is especially important for systems with spin density waves, a striking example of which are iron-containing pnictides.