Revising a generalized spin current theory for the magnetoelectric effect in multiferroics

Microscopic aspects of ferroelectricity are canonically related to polar atomic displacements that break inversion symmetry of the crystal, leading to a non-zero net electric dipole moment. However, there is a special class of magnetic materials called multiferroics where inversion symmetry breaking occurs by a magnetic order stabilized in an otherwise crystallographically centrosymmetric lattice. The magnetically induced electric polarization can display complex forms of magnetoelectric coupling to the underlying magnetic texture, and its practical realization is one of the key directions towards achieving the cross-control of ferroelectric properties and magnetism in new generation electronic devices. Thus, understanding the microscopic origin of multiferroicity is a foremost goal of both fundamental and practical importance.