  Logical devices based on spin waves offer the potential to avoid dissipation
mechanisms that limit devices based on either the charge or spin of mobile
electrons. Multiferroic magnetoelectrics, which are materials that combine
ferroelectric and magnetic order, allow direct switching of magnetic order and
thence of spin-wave properties using an applied electric field. The intrinsic
coupling between polarization and magnetic moments, generated by strong
electronic correlations in these multiferroic materials, is argued to provide
new approaches to spin-wave injection and spin-wave switching using applied
voltages with no external magnetic field. These effects are shown to arise in a
phenomenological Landau theory of coupled electronic and magnetic orders in
multiferroic BiFeO3, and found to depend subtly on differences between the
crystalline and film states of this material.
