Due to only partially filled electronic d shells, the physics of transition-metal compounds is characterized by a complex interplay of electronic spin, orbital, and charge, as well as of the lattice degrees of freedom.

These electronic correlations give rise to various ordering phenomena, induce metal-to-insulator transitions, superconductivity at rather high temperatures, colossal magneto resistance, heavy-fermion like behavior, and electronic phase separation. Recently, the concomitant appearance of ferroelectricity and ferromagnetism or, more generally, the simultaneous onset of a permanent electric polarization and magnetic order, which is observed in a number of transition metal oxides and chalcogenides, came into the focus of modern solid-state research. Such systems with strong magnetoelectric coupling belong to the class of multiferroic materials, which exhibit more than one ferroic order parameter (including also ferroelasticity and ferrotoroidicity).

Materials with strong magnetoelectric coupling are of high interest for a possible application in modern electronic circuits as they allow to switch the electric polarization by means of a magnetic field as well as vice versa the magnetization by means of an electric field.