Program Highlights

Designer Superlattices with Multifunctional Properties

Yong Wang, J. D. Burton, and Evgeny Tsymbal
Nebraska MRSEC

 J.W. Seo, L.F.N. Ah Qune, and C. Panagopoulos
Nanyang Technological University, Singapore

 K. Rogdakis and Z. Viskadourakis
Institute of Electronic Structure and Laser, Heraklion, Greece

E. Choi and J. Lee 
Sungkyunkwan University, Suwon, Republic of Korea

The electronic elements that make up modern technology are packed so tightly and use so much energy that we are quickly approaching a limit on the scalability of future of devices. Researchers at the Nebraska MRSEC are exploring novel routes to circumnavigate the impending plateau in technological progress. One avenue to do this is to find materials in which electrical polarization (ferroelectricity) is intimately coupled to magnetization (ferromagnetism), allowing for low power electrical control of magnetic properties. Only a very few such materials exist, so as an alternative to searching for materials is to design them from scratch.

The international team of researchers led by Christos Panagopoulos of Nanyang Technological University, Singapore, fabricated a series of multilayered structures known as superlattices.  Each layer of the superlattice consists of one of three different complex oxides as shown in figure. It was discovered that although all three components are non-ferromagnetic and non-ferroelectric on their own, the combination turns out to be both ferromagnetic and ferroelectric, with a strong coupling between the two properties. [Nature Communications 3, 1064 (2012)].

The origin of this surprising behavior was uncovered by sophisticated calculations by Nebraska MRSEC researchers. They found that charges build up at the interfaces between the different materials, and that these charges can be shifted from one interface to another by applied voltage, giving rise to a switchable polarization. Furthermore, the shifting of these charges gives rise to a change in the net magnetization, which is the origin of the magnetoelectric coupling observed in the experiments.

This kind of engineering of novel properties at complex interfaces is an exciting prospect, and one which will guide future studies within the Nebraska MRSEC and collaborators.

These programs are supported by the National Science Foundation, Division of Materials Research, Materials Research Science and Engineering Program, Grant 0820521.

Atomic structure of a manganite superlattice. The arrows indicate the magnetic moment on the Manganese atoms (magenta). Red, blue, green, and yellow spheres are Oxygen, Lanthanum, Strontium and Neodymium atoms, respectively.