Interface engineering enables a path forward for magnetoelectric multiferroics

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(Left panel): Magnetization vs. magnetic field for superlattice measured from (blue) ±0.5 T and (red, and inset) ±7 T at 10 K. (Right panel): The temperature dependence of the magnetizations for LSMO (circles) and BFO (triangles) layers in the superlattice, (squares) the thickness-­‐weighted average of these magnetization and (diamonds) the moment of the sample measured with magnetometry normalized by the volume of the superlattice film.

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Los Alamos scientists and collaborators have discovered a way to realize magnetoelectric coupling and net magnetic moment in antiferromagnetic BiFeO3 (BFO). This finding has potential utility for designing high-density data storage platforms of the future. The journal Scientific Reports reported the research.

 

BFO has outstanding ferroelectric properties. However, there is virtually no net moment to interact with an applied magnetic field. This lack of a magnetic handle impedes its development for potential applications. Therefore, the researchers developed a composite of two materials [La0.7Sr0.3MnO3 (LSMO) and BFO], neither of which independently exhibits a dielectric response to a magnetic field. Polarized neutron reflectometry measurements of the composite reveal significant net uncompensated magnetization in BFO. The authors conclude that the large uncompensated magnetization of BFO in the superlattice is a consequence of unique features associated with the superlattice, e.g., its growth, strain, architecture, proximity to a ferromagnet, etc. Below 179 K, LSMO is ferromagnetic and BFO exhibits net uncompensated magnetization; the magnetization of BFO is opposite to that of the LSMO. The magnetic order parameters have the same dependence with temperature, suggesting that LMSO induces the uncompensated magnetization of BFO. The magnetization enables a magnetic field to change the dielectric properties of the superlattice. The team cited this phenomenon as an example of synthetic magnetoelectric coupling.

 

The finding represents a new path to produce synthetic magnetoelectric coupling in a nanocomposite at 10 K. This approach means that rather than requiring discovery of a single-phase multiferroic for useful applications, the challenge becomes more manageable – one of using interface engineering to couple dissimilar materials intimately. The team concludes that the controlled creation of magnetic moment in BFO is an important step toward the design and implementation of integrated oxide devices for next generation magnetoelectric data storage platforms.

 

Reference: “Synthetic Magnetoelectric Coupling in a Nanocomposite Multiferroic,” Scientific Reports 5, 9089 (2015); doi: 10.1038/srep09089. Authors: Prashant Jain (Materials Synthesis and Integrated Devices, MPA-11); Qiang Wang, Z. Bi, and Quanxi Jia (MPA-CINT); Towfiq Ahmed and Jianxin Zhu (Physics of Condensed Matter and Complex Systems, T-4); Michael Fitzsimmons (formerly of Lujan Center, LANSCE-LC); M. Moldan (Universidad Complutense de Madrid, Spain); A. Glavic (Oak Ridge National Laboratory); C. Urban (University of California – San Diego), and M. Varela (Universidad Complutense de Madrid and Oak Ridge National Laboratory).

 

The Laboratory Directed Research and Development (LDRD) program funded the work, which was performed, in part, at the Center for Integrated Nanotechnologies (CINT), an Office of Science User Facility operated for the DOE Office of Science. This work has benefited from the use of the Spallation Neutron Source (Oak Ridge National Laboratory) and the LANSCE Lujan Center (Los Alamos National Laboratory), which were at the time funded by the Scientific User Facilities Division of the DOE’s Office of Basic Energy Sciences; and the National High Magnetic Field Laboratory (at Los Alamos), which the National Science Foundation sponsors. The work supports the Laboratory’s Energy Security mission area and the Materials for the Future science pillar through the use of materials with tailored functionality to enable technological innovations in information storage, sensing, and computing. Technical contact: Quanxi Jia