12 - Progress toward magnetoelectric spintronics

Abstract

Ferromagnetic materials can be used for information storage because they have bistable states that can be seen as “1” and “0.” In magnetic-based memory devices such as magnetic tapes, magnetic hard drives, and magnetic random access memory, information is stored by switching the magnetic state using a magnetic field that is generated by electric currents. Such a field should, however, be larger enough to overcome the coercive field of the materials and thus consumes a large amount of power. Although the spin transfer torque generated by the spin current lowers the current requirement of switching one bit by orders of magnitude, the voltage-controlled spintronics is greatly demanded for ultraminiature and power-efficient devices. Multiferroic materials and magnetoelectric heterostructures have attracted intensified research interest because of the strong magnetoelectric coupling that can control the magnetism of ferromagnetic materials by applied voltage. Different magnetoelectric coupling mechanisms and strain-mediated, interfacial charge-mediated, and exchange coupled magnetoelectric effects are discussed in this chapter. The ferroelastic nonvolatile switching of magnetism in artificial ferromagnetic/ferroelectric magnetoelelctric heterostructures is a focus. The localized voltage control of the magnetic bit offers great opportunity to miniaturize spintronic devices. In traditional magnetic random access memory devices, a reduced Oersted field on the neighboring bit would also apply. With the presence of multiferroic or magnetoelectric materials, spin is controlled by an electric field, which opens new opportunities for voltage control of spintronic devices. In such novel spintronics the spin and charge, or magnetic and ferroelectric degrees of freedom, are coupled to achieve voltage control of the magnetic state with ultralow energy consumption.