Abstract

Materials that exhibit simultaneous order in their electric and magnetic ground states hold promise for use in next-generation memory devices in which electric fields control magnetism1,2. Such materials are exceedingly rare, however, owing to competing requirements for displacive ferroelectricity and magnetism3. Despite the recent identification of several new multiferroic materials and magnetoelectric coupling mechanisms4,5,6,7,8,9,10,11,12,13,14,15, known single-phase multiferroics remain limited by antiferromagnetic or weak ferromagnetic alignments, by a lack of coupling between the order parameters, or by having properties that emerge only well below room temperature, precluding device applications2. Here we present a methodology for constructing single-phase multiferroic materials in which ferroelectricity and strong magnetic ordering are coupled near room temperature. Starting with hexagonal LuFeO3—the geometric ferroelectric with the greatest known planar rumpling16—we introduce individual monolayers of FeO during growth to construct formula-unit-thick syntactic layers of ferrimagnetic LuFe2O4 (refs 17, 18) within the LuFeO3 matrix, that is, (LuFeO3)m/(LuFe2O4)1 superlattices. The severe rumpling imposed by the neighbouring LuFeO3 drives the ferrimagnetic LuFe2O4 into a simultaneously ferroelectric state, while also reducing the LuFe2O4 spin frustration. This increases the magnetic transition temperature substantially—from 240 kelvin for LuFe2O4 (ref. 18) to 281 kelvin for (LuFeO3)9/(LuFe2O4)1. Moreover, the ferroelectric order couples to the ferrimagnetism, enabling direct electric-field control of magnetism at 200 kelvin. Our results demonstrate a design methodology for creating higher-temperature magnetoelectric multiferroics by exploiting a combination of geometric frustration, lattice distortions and epitaxial engineering.

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Acknowledgements

We acknowledge discussions with G. Stiehl, R. Haislmaier, A. SenGupta, V. Gopalan, W. Wang, W. Wu and E. Barnard and technical support with the electron microscopy from E. J. Kirkland, M. Thomas and J. Grazul. Research primarily supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Award No. DE-SC0002334, which supported the work of J.A.Mu. (2010–2014), C.M.B., M.E.H., J.A.Mo., H.D., A.F.R., R.He., Q.M., H.P., R.M., C.J.F., P.S., D.A.M. and D.G.S. Substrate preparation was performed in part at the Cornell NanoScale Facility, a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the National Science Foundation (Grant ECCS-15420819). The electron microscopy studies made use of the electron microscopy facility of the Cornell Center for Materials Research, a National Science Foundation (NSF) Materials Research Science and Engineering Centers programme (DMR 1120296) and NSF IMR-0417392. X-ray dichroism was performed at the Advanced Light Source at Lawrence Berkeley National Laboratory. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-AC02-05CH11231. J.A.Mu. acknowledges fellowship support from the Army Research Office in the form of a National Defense Science and Engineering Graduate Fellowship and from the National Science Foundation in the form of a Graduate Research Fellowship. J.A.Mu. was funded (July 2015–) by C-SPINS, one of six centres of STARnet, a Semiconductor Research Corporation programme, sponsored by MARCO and DARPA. J.T.H. acknowledges support from the Semiconductor Research Corporation (SRC) under grant 2014-IN-2534. J.D.C. acknowledges support from SRC-FAME, one of six centres of STARnet, a Semiconductor Research Corporation programme sponsored by MARCO and DARPA. S.M.D. acknowledges the support of a National Research Council NIST postdoctoral research associateship. Z.L. acknowledges support from the NSF under Grant No. EEC-1160504 NSF Nanosystems Engineering Research Center for Translational Applications of Nanoscale Multiferroic Systems (TANMS). A.F. is supported by the Swiss National Science Foundation. R.Ho. and L.F.K. acknowledge support by the David and Lucile Packard Foundation. E.P. acknowledges support from the National Science Foundation in the form of a Graduate Research Fellowship (DGE-1144153). Certain commercial equipment, instruments, or materials are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

Author information

Author notes

    • Julia A. Mundy
    • , Charles M. Brooks
    •  & Megan E. Holtz

    These authors contributed equally to this work.

Affiliations

  1. School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA

    • Julia A. Mundy
    • , Megan E. Holtz
    • , Hena Das
    • , Alejandro F. Rébola
    • , Robert Hovden
    • , Elliot Padgett
    • , Qingyun Mao
    • , Lena F. Kourkoutis
    • , Craig J. Fennie
    •  & David A. Muller
  2. Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA

    • Charles M. Brooks
    • , John T. Heron
    • , Rainer Held
    • , Hanjong Paik
    •  & Darrell G. Schlom
  3. Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA

    • Jarrett A. Moyer
    •  & Peter Schiffer
  4. Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48103, USA

    • John T. Heron
  5. Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA

    • James D. Clarkson
    • , Zhiqi Liu
    •  & Ramamoorthy Ramesh
  6. NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA

    • Steven M. Disseler
    • , Julie A. Borchers
    •  & William D. Ratcliff
  7. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Alan Farhan
    • , Elke Arenholz
    •  & Andreas Scholl
  8. Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA

    • Rajiv Misra
  9. Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA

    • Lena F. Kourkoutis
    • , David A. Muller
    •  & Darrell G. Schlom
  10. Department of Physics, University of California, Berkeley, California 94720, USA

    • Ramamoorthy Ramesh
  11. Materials Sciences Division, Lawrence Berkeley National Laboratory, California 94720, USA

    • Ramamoorthy Ramesh

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Contributions

The thin films were synthesized by C.M.B. and J.A.Mu. with assistance from R.He. and H.P. DFT calculations were performed by H.D., A.F.R. and C.J.F. The films were characterized by SQUID by J.A.Mo., R.M. and P.S.; by STEM by M.E.H., J.A.Mu., R.Ho., E.P., L.F.K. and D.A.M.; by variable-temperature STEM by Q.M., M.E.H. and D.A.M.; by neutron scattering by S.M.D., J.A.B. and W.D.R.; by transport by J.T.H.; by PFM by J.D.C., J.T.H. and R.R.; by X-ray spectroscopy by J.A.Mu., Z.L. and E.A.; by PEEM by A.F., Z.L., J.D.C., R.R. and A.S. J.A.Mu., C.J.F. and D.G.S. wrote the manuscript. The study was conceived and guided by D.G.S. All authors discussed results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Darrell G. Schlom.

Reviewer Information Nature thanks M. Fiebig, T. Kimura and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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https://doi.org/10.1038/nature19343

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