Layered two-phase magnetoelectric materials

Multiferroic materials have attracted great interest for having more than one primary ferroic-order parameter in a single material. Magnetoelectric (ME) material is one of the multiferroic materials that produces a voltage under a stimulation of magnetic field and has stirred up much interest recently due to its potential applications in multifunctional devices. Natural single-phase multiferroic compounds are rare, and the ME effect is either weak or occurs at a too low temperature for practical applications. A two-phase ME material incorporates ferroelectric and ferri-/ferromagnetic phases into one to yield giant ME effect at room temperature, rendering it practically applicable. The elastic coupling interaction between the magnetostrictive phase and piezoelectric phase leads to giant ME response of these ME materials, such as ferrite and piezoelectric ceramics, magnetic metals/alloys, and piezoelectric ceramics. When a direct current (DC) bias field is superimposed with a small oscillating alternating field, an electric polarization is induced and/or a magnetization polarization appears. For application in microelectronic devices, nanostructured composite coatings of ferroelectric and magnetostrictive materials have been deposited on a substrate. In this chapter, multiferroism and magnetoelectricity are explained; experimental and theoretical aspects of laminate and multilayer structured ME composites are discussed; and transducers, sensors, microwave devices, etc. are introduced from the application point of view.