R esearch on the magnetoelectric (ME) eff ect, discovered more than a century ago [1], progressed through pioneering work in the 1950s and 1960s, and has now seen a resurgence driven by long-term technological aspirations. With the trends toward device miniaturization, there is ever-increasing interest in combining electronic and magnetic properties into multifunctional materials to produce a single device component that can perform more than one task. Multiferroic ME materials are particularly appealing not only because they have the properties of their parent compounds, but also because interactions between the magnetic and electric orders lead to additional functionalities.From the viewpoint of material constituents, multiferroic ME materials can essentially be divided into two types: single-phase [2,3] and composite [4,5]. According to the original defi nition, a singlephase multiferroic material is one that possesses at least two of the 'ferroic' properties, such as ferroelectricity, ferromagnetism or ferroelasticity. While ME composites are multiphase materials composed of diff erent phases, neither phase supports the ME eff ect.Magnetoelectric coupling describes the infl uence of a magnetic (electric) fi eld on the polarization (magnetization) of a material. It may arise directly between the two order parameters as in single-phase multiferroics, or indirectly via strain/stress as in ME composites. Several recent articles have summarized and reviewed research progress in single-phase multiferroic ME materials [2,3], and accordingly, this review will instead focus on composite multiferroic materials.Th e ME eff ect in composite materials is known as a product tensor property, fi rst proposed by van Suchtelen in 1972 [5], that results from the cross interaction between the two phases in the composite. As illustrated schematically in Figure 1, the composite ME eff ect is a result of the product of the magnetostrictive eff ect (magnetic/mechanical eff ect) in the magnetic phase and the piezoelectric eff ect (mechanical/ electrical eff ect) in the piezoelectric phase.
Multiferroic magnetoelectric composite nanostructuresYao Wang, Jiamian Hu, Yuanhua Lin and Ce-Wen Nan * Tsinghua University, ChinaMultiferroics are attracting increasing interest and provoking much research activity driven by the profound physics of these materials, the coexistence and coupling of ferroelectric and magnetic orders, and the potential applications in novel multifunctional devices such as sensors, transducers, memories and spintronics. Multiferroic magnetoelectric (ME) composite systems, such as ferromagnetic-ferroelectric heterostructures, which off er a novel route for integrating ferroelectric and ferromagnetism, have been widely studied in recent years. In these ME composite systems, ME coupling is strain-mediated, that is, the strain induced in one component, either by magnetostriction in the ferromagnetic or by the piezoelectric eff ect in the ferroelectric, is transferred to the other component, altering the polarization or ma...