Multiferroics as Quantum Electromagnets

The term “electromagnetism” comes from the fact that the electric and magnetic fields are generally not independent of one another. A changing magnetic field produces an electric field (electromagnetic induction), whereas the motion of electric charges, or electric current, generates a magnetic field (the Biot-Savart law). Typically, electromagnets are wire coils or loops, which tend to be bulky and difficult to fabricate. Would it be possible to devise an electromagnet made from a nano- or micrometer-scale material (not in the form of a coil) that could be activated by simply applying an electric field or current? The answer is perhaps yes, but the issue is not straightforward at all. The magnetoelectric (ME) effect in a solid—that is, the induction of a magnetization (M) by means of an electric field and the induction of an electric polarization (P) by means of a magnetic field—was presumed to exist by Pierre Curie (1), who considered the analogy of the electromagnetic phenomena in a vacuum and in a solid. This analogy is important today from the standpoint of applications: The highly efficient control of magnetism by an electric field or electric current in a solid may advance the technology of spin-electronics (spintronics) technology, such as magnetic storage and magnetic random-access memory. Since the ME effect was first confirmed in the 1960s by Russian scientists, many magnetic materials have been shown to produce this effect (2). Nevertheless, the magnitude of the observed ME effect has been too small for practical devices.