Introduction to magnetoelectric coupling and multiferroic films

There is an increasing understanding of the mechanisms underlying the development of magnetoelectric coupling and multiferroic order in both single-phase and composite materials. The investigations underlying this advance include a range of studies on thin films, which are expected to play an important role in the development of novel magnetoelectric devices. The properties of both single-phase and composite systems are widely studied. While single-phase materials can exhibit rich spin-charge coupling physics, the magnetizations, polarizations, and transition temperatures are often too small to be innately useful for device design. Conversely, a number of ferromagnetic-piezoelectric composites can show strong magnetoelectric coupling at ambient temperatures, which develops as a product-property mediated by elastic deformation, making these systems more directly amenable to fabricating devices. In this review, we provide a short overview of the mechanisms for magnetoelectric coupling in multiferroics, together with a discussion of how this magnetoelectric coupling is relevant for designing new multiferroic devices, including magnetic field sensors, dual electric and magnetic field tunable microwave and millimetre wave devices and miniature antennas. We present a brief summary of some of the significant results in studies on thin-film multiferroics, with an emphasis on single-phase materials, and covering systems where the magnetic and ferroelectric transitions fall at the same temperature as well as systems where they fall at different temperatures.