As computers and cell phones become smarter and faster, they use more electricity. More electricity means more heat. Dispelling that heat uses more energy. New materials that couple electric and magnetic states of a material could break this cycle. Scientists created a new material that displays electrically controlled magnetism at room temperature. They created the material by assembling alternating atomic layers of two oxide materials. They exploited geometric factors and atomic lattice distortions between the alternate materials.
The study provides the insights needed to make materials with both magnetic and polarizable electronic properties at room temperature. With this research, scientists can now engineer artificial materials that have the desired properties. These materials could improve memory storage devices and sensors.
It is rare to find materials that operate at room temperature and display strong “multiferroic coupling” — a property that allows an electric field to control the direction of the electronic spin and a magnetic field that controls positive/negative electronic charge. Thus, the material has both ferroelectricity and ferromagnetism. Now, scientists have designed a new material that can operate at room temperature (281K). Using a synthesis approach with atomic control called molecular beam epitaxy, the team assembled an artificial material with alternating layers of lutetium iron oxide (LuFeO3, a ferroelectric material) and LuFe2O4 (a ferrimagnetic material). The team varied the number of atomic sheets in the LuFeO3 layer from 1 to 10. With 9 atomic sheets in the LuFeO3 layer, they induced a ferroelectric state in the LuFe2O4while simultaneously increasing the magnetic transition temperature from 240K (-27 F) in LuFe2O4 to 281K (46 F). The ferroelectric coupling to ferrimagnetism enables control of the magnetism by electric fields at 200K (-100 F). The team used methods insensitive to magnetic impurities (e.g., neutron diffraction) or electrical leakage (e.g., high-resolution electron microscopy) to substantiate the results, which were consistent with first-principles calculations.
The research was primarily supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (conceiving the project, thin film synthesis, variable temperature scanning transmission electron microscopy, density functional theory, and characterization), including support of the Advanced Light Source, an Office of Science user facility (x-ray dichroism); Semiconductor Research Corporation provided partial support (for transport measurements, some photoemission electron microscopy and some piezoresponse force microscopy). Support for graduate student and postdoctoral fellowships came from the following: Army Research Office, National Science Foundation (NSF), Swiss National Science Foundation, David and Lucile Packard Foundation, Semiconductor Research Corporation, National Research Council, and National Institute of Standards and Technology (NIST). Other facilities were supported by the NSF (electron microscopy facility at Cornell, Cornell NanoScale Facility) and NIST (neutron scattering).
J.A. Mundy, C.M. Brooks, M.E. Holtz, J.A. Moyer, H. Das, A.F. Rebola, J.T. Heron, J.D. Clarkson, S.M. Disseler, Z. Liu, A. Farhan, R. Held, R. Hovden, E.R. Padgett, Q. Mao, H. Paik, R. Misra, L.K. Kourkoutis, E. Arenholz, A. Scholl, J.A. Brochers, W.D. Ratcliff, R. Ramesh, C.F. Fennie, P. Schiffer, D.A. Muller, and D.G. Schlom, “Atomically engineered ferroic layers yield a room-temperature magnetoelectric multiferroic.” Nature 537, 526 (2016). [DOI: 10.1038/nature19343]