Multiferroics and applications

Much academic and industrial effort has been devoted to the study of multiferroics, but if related technologies are to have real-world impact, market awareness and reproducibility are also key.

Nian Sun, a professor at Northeastern University (Electrical and Computer Engineering Department), talks to Nature Materials about the potential applications of multiferroic materials, and issues associated with commercializing these technologies.

Topological structures have considerable potential in nanoelectronics and new device concepts. They are key to the design and understanding of novel functionalities in ferroic materials — that is, materials that have one or more types of built-in order such as magnetic, ferroelectric, ferroelastic and multiferroic materials.

Multiferroic quantum criticality — associated with the merging of two distinct quantum critical points — is explored, with implications for fundamental physics and low-temperature applications.

Magnetoelectric multiferroics, where magnetic properties are manipulated by electric field and vice versa, could lead to improved electronic devices. Here, advances in materials, characterisation and modelling, and usage in applications are reviewed.

The phenomenology of multiferroic quantum criticality, where both ferroelectric and magnetic order parameters are tuned by quantum fluctuations, is drawn out. Non-thermal tuning parameters such as alloying and strain are explored and material realizations proposed.

The interplay between the electronic and magnetic degrees of freedom in multiferroic materials offers promise for a range of applications. Now, a technique for imaging the magnetoelectric domains directly is developed, and demonstrated on the hexagonal manganite ErMnO₃.

The ferroelectric properties of BiFeO₃ have been the subject of extensive study. Using a range of experimental tools and numerical modelling, it is now shown that its ferroic properties can also be manipulated by strain effects, giving rise to a variety of magnonic phenomena.

In multiferroics ferroelectricity and magnetism are coupled, but the coupling is often rather weak. As is now shown for a perovskite oxide, composite domain walls can lead to a strong coupling of electricity and magnetism, highlighting the importance of domain walls for practical applications using multiferroics.